diff --git a/src/IUVData.ts b/src/IUVData.ts
index acec02715..ae1dbe00b 100644
--- a/src/IUVData.ts
+++ b/src/IUVData.ts
@@ -4,8 +4,11 @@ import { YouTubeData } from "./content-handlers/youtube/YouTubeData";
 import { ILocale } from "./content-handlers/iiif/modules/uv-shared-module/ILocale";
 import { BaseConfig } from "./content-handlers/iiif/BaseConfig";
 
-export interface IUVData extends IIIFData, EPubData, YouTubeData {
-  config?: BaseConfig; // do not pass this on initialisation, internal use only
+export interface IUVData<T extends BaseConfig>
+  extends IIIFData,
+    EPubData,
+    YouTubeData {
+  config?: T; // do not pass this on initialisation, internal use only
   debug?: boolean;
   embedded?: boolean;
   isReload?: boolean;
diff --git a/src/UniversalViewer.ts b/src/UniversalViewer.ts
index 190a75216..8b563eeb6 100644
--- a/src/UniversalViewer.ts
+++ b/src/UniversalViewer.ts
@@ -4,7 +4,7 @@ import BaseContentHandler, { EventListener } from "./BaseContentHandler";
 
 export interface IUVOptions {
   target: HTMLElement;
-  data: IUVData;
+  data: IUVData<any>;
 }
 
 enum ContentType {
@@ -29,9 +29,9 @@ const ContentHandler: IContentHandlerRegistry = {
     ),
 };
 
-export class UniversalViewer extends BaseContentHandler<IUVData> {
+export class UniversalViewer extends BaseContentHandler<IUVData<any>> {
   private _contentType: ContentType = ContentType.UNKNOWN;
-  private _assignedContentHandler: IContentHandler<IUVData>;
+  private _assignedContentHandler: IContentHandler<IUVData<any>>;
   private _externalEventListeners: EventListener[] = [];
 
   constructor(public options: IUVOptions) {
@@ -51,7 +51,7 @@ export class UniversalViewer extends BaseContentHandler<IUVData> {
     });
   }
 
-  private async _assignContentHandler(data: IUVData): Promise<boolean> {
+  private async _assignContentHandler(data: IUVData<any>): Promise<boolean> {
     let contentType: ContentType;
 
     if (data[ContentType.IIIFLEGACY]) {
@@ -91,7 +91,7 @@ export class UniversalViewer extends BaseContentHandler<IUVData> {
     return handlerChanged;
   }
 
-  public set(data: IUVData, initial?: boolean): void {
+  public set(data: IUVData<any>, initial?: boolean): void {
     // content type may have changed
     this._assignContentHandler(data).then((handlerChanged: boolean) => {
       if (handlerChanged) {
diff --git a/src/Utils.ts b/src/Utils.ts
index de5619660..2e2190554 100644
--- a/src/Utils.ts
+++ b/src/Utils.ts
@@ -36,8 +36,8 @@ export const debounce = (callback: (args: any) => void, wait: number) => {
 };
 
 export const propertiesChanged = (
-  newData: IUVData,
-  currentData: IUVData,
+  newData: IUVData<any>,
+  currentData: IUVData<any>,
   properties: string[]
 ): boolean => {
   let propChanged: boolean = false;
@@ -53,8 +53,8 @@ export const propertiesChanged = (
 };
 
 export const propertyChanged = (
-  newData: IUVData,
-  currentData: IUVData,
+  newData: IUVData<any>,
+  currentData: IUVData<any>,
   propertyName: string
 ): boolean => {
   return currentData[propertyName] !== newData[propertyName];
diff --git a/src/content-handlers/iiif/BaseConfig.ts b/src/content-handlers/iiif/BaseConfig.ts
index 3140292c4..edf1af59c 100644
--- a/src/content-handlers/iiif/BaseConfig.ts
+++ b/src/content-handlers/iiif/BaseConfig.ts
@@ -93,9 +93,6 @@ export type Options = {
   /** Determines if arrow keys can be used to navigate */
   useArrowKeysToNavigate?: boolean;
 
-  /** Determines if PDF.js should be used for PDF rendering */
-  usePdfJs?: boolean;
-
   /** Determines if zoom to search result is enabled */
   zoomToSearchResultEnabled?: boolean;
 
diff --git a/src/content-handlers/iiif/IIIFContentHandler.ts b/src/content-handlers/iiif/IIIFContentHandler.ts
index cad538ba5..9cf0fe373 100644
--- a/src/content-handlers/iiif/IIIFContentHandler.ts
+++ b/src/content-handlers/iiif/IIIFContentHandler.ts
@@ -36,64 +36,64 @@ const Extension: IExtensionRegistry = {
     name: "uv-av-extension",
     loader: () =>
       /* webpackMode: "lazy" */ import(
-      "./extensions/uv-av-extension/Extension"
-    ),
+        "./extensions/uv-av-extension/Extension"
+      ),
   },
   ALEPH: {
     name: "uv-aleph-extension",
     loader: () =>
       /* webpackMode: "lazy" */ import(
-      "./extensions/uv-aleph-extension/Extension"
-    ),
+        "./extensions/uv-aleph-extension/Extension"
+      ),
   },
   DEFAULT: {
     name: "uv-default-extension",
     loader: () =>
       /* webpackMode: "lazy" */ import(
-      "./extensions/uv-default-extension/Extension"
-    ),
+        "./extensions/uv-default-extension/Extension"
+      ),
   },
   EBOOK: {
     name: "uv-ebook-extension",
     loader: () =>
       /* webpackMode: "lazy" */ import(
-      "./extensions/uv-ebook-extension/Extension"
-    ),
+        "./extensions/uv-ebook-extension/Extension"
+      ),
   },
   MEDIAELEMENT: {
     name: "uv-mediaelement-extension",
     loader: () =>
       /* webpackMode: "lazy" */ import(
-      "./extensions/uv-mediaelement-extension/Extension"
-    ),
+        "./extensions/uv-mediaelement-extension/Extension"
+      ),
   },
   MODELVIEWER: {
     name: "uv-model-viewer-extension",
     loader: () =>
       /* webpackMode: "lazy" */ import(
-      "./extensions/uv-model-viewer-extension/Extension"
-    ),
+        "./extensions/uv-model-viewer-extension/Extension"
+      ),
   },
   OSD: {
     name: "uv-openseadragon-extension",
     loader: () =>
       /* webpackMode: "lazy" */ import(
-      "./extensions/uv-openseadragon-extension/Extension"
-    ),
+        "./extensions/uv-openseadragon-extension/Extension"
+      ),
   },
   PDF: {
     name: "uv-pdf-extension",
     loader: () =>
       /* webpackMode: "lazy" */ import(
-      "./extensions/uv-pdf-extension/Extension"
-    ),
+        "./extensions/uv-pdf-extension/Extension"
+      ),
   },
   SLIDEATLAS: {
     name: "uv-openseadragon-extension",
     loader: () =>
       /* webpackMode: "lazy" */ import(
-      "./extensions/uv-openseadragon-extension/Extension"
-    ),
+        "./extensions/uv-openseadragon-extension/Extension"
+      ),
   },
 };
 
@@ -196,7 +196,7 @@ export default class IIIFContentHandler extends BaseContentHandler<IIIFData>
     return this._getExtensionByType(this._extensionRegistry[format], format);
   }
 
-  public set(data: IUVData, initial?: boolean): void {
+  public set(data: IUVData<any>, initial?: boolean): void {
     if (initial) {
       this.extra.initial = true;
     }
@@ -210,7 +210,11 @@ export default class IIIFContentHandler extends BaseContentHandler<IIIFData>
       this._reload(data);
     } else {
       // changing any of these data properties forces the UV to reload.
-      const newData: IUVData = Object.assign({}, this.extension.data, data);
+      const newData: IUVData<any> = Object.assign(
+        {},
+        this.extension.data,
+        data
+      );
       if (
         newData.isReload ||
         newData.iiifManifestId !== this.extension.data.iiifManifestId ||
@@ -269,12 +273,12 @@ export default class IIIFContentHandler extends BaseContentHandler<IIIFData>
     // $elem.attr("class", "");
   }
 
-  private async _reload(data: IUVData): Promise<void> {
+  private async _reload(data: IUVData<any>): Promise<void> {
     this._pubsub.dispose(); // remove any existing event listeners
 
     data.target = ""; // clear target
 
-    this.subscribe(Events.RELOAD, (data?: IUVData) => {
+    this.subscribe(Events.RELOAD, (data?: IUVData<any>) => {
       this.fire(Events.RELOAD, data);
     });
 
@@ -384,7 +388,10 @@ export default class IIIFContentHandler extends BaseContentHandler<IIIFData>
       }
 
       // import the config file
-      let config = await (extension as any).loadConfig(data.locales[0].name, extension?.type.name);
+      let config = await (extension as any).loadConfig(
+        data.locales[0].name,
+        extension?.type.name
+      );
 
       data.config = await that.configure(config);
 
@@ -401,7 +408,7 @@ export default class IIIFContentHandler extends BaseContentHandler<IIIFData>
 
   private _createExtension(
     extension: any,
-    data: IUVData,
+    data: IUVData<any>,
     helper: Helper
   ): void {
     this.extension = extension;
diff --git a/src/content-handlers/iiif/URLAdapter.ts b/src/content-handlers/iiif/URLAdapter.ts
index 33cf11a05..f66bd43c9 100644
--- a/src/content-handlers/iiif/URLAdapter.ts
+++ b/src/content-handlers/iiif/URLAdapter.ts
@@ -40,7 +40,7 @@ export class URLAdapter extends UVAdapter {
     }
   }
 
-  public getInitialData(overrides?: IUVData): IUVData {
+  public getInitialData(overrides?: IUVData<any>): IUVData<any> {
     const formattedLocales: Array<{ label?: string; name: string }> = [];
     const locales = this.get<string>("locales", "");
     if (locales) {
@@ -189,7 +189,7 @@ export class URLAdapter extends UVAdapter {
     uv.on(
       IIIFEvents.RANGE_CHANGE,
       (range) => {
-        const rangeId = !range || typeof range === 'string' ? range : range.id;
+        const rangeId = !range || typeof range === "string" ? range : range.id;
         this.set("rid", rangeId);
       },
       false
diff --git a/src/content-handlers/iiif/extensions/uv-aleph-extension/Extension.ts b/src/content-handlers/iiif/extensions/uv-aleph-extension/Extension.ts
index ca07524c6..536d13d9d 100644
--- a/src/content-handlers/iiif/extensions/uv-aleph-extension/Extension.ts
+++ b/src/content-handlers/iiif/extensions/uv-aleph-extension/Extension.ts
@@ -15,7 +15,7 @@ import "./theme/theme.less";
 import defaultConfig from "./config/config.json";
 import { Config } from "./config/Config";
 
-export default class Extension extends BaseExtension
+export default class Extension extends BaseExtension<Config>
   implements IAlephExtension {
   $downloadDialogue: JQuery;
   $multiSelectDialogue: JQuery;
diff --git a/src/content-handlers/iiif/extensions/uv-aleph-extension/IAlephExtensionData.ts b/src/content-handlers/iiif/extensions/uv-aleph-extension/IAlephExtensionData.ts
index 4e70277b9..172116023 100644
--- a/src/content-handlers/iiif/extensions/uv-aleph-extension/IAlephExtensionData.ts
+++ b/src/content-handlers/iiif/extensions/uv-aleph-extension/IAlephExtensionData.ts
@@ -1,3 +1,4 @@
 import { IUVData } from "../../../../IUVData";
+import { Config } from "./config/Config";
 
-export interface IAlephExtensionData extends IUVData {}
+export interface IAlephExtensionData extends IUVData<Config> {}
diff --git a/src/content-handlers/iiif/extensions/uv-av-extension/Extension.ts b/src/content-handlers/iiif/extensions/uv-av-extension/Extension.ts
index fad5a67c2..fb583aa20 100644
--- a/src/content-handlers/iiif/extensions/uv-av-extension/Extension.ts
+++ b/src/content-handlers/iiif/extensions/uv-av-extension/Extension.ts
@@ -17,7 +17,8 @@ import "./theme/theme.less";
 import defaultConfig from "./config/config.json";
 import { Config } from "./config/Config";
 
-export default class Extension extends BaseExtension implements IAVExtension {
+export default class Extension extends BaseExtension<Config>
+  implements IAVExtension {
   $downloadDialogue: JQuery;
   $multiSelectDialogue: JQuery;
   $settingsDialogue: JQuery;
diff --git a/src/content-handlers/iiif/extensions/uv-av-extension/IAVExtensionData.ts b/src/content-handlers/iiif/extensions/uv-av-extension/IAVExtensionData.ts
index 94f4851a2..7a22fa7d9 100644
--- a/src/content-handlers/iiif/extensions/uv-av-extension/IAVExtensionData.ts
+++ b/src/content-handlers/iiif/extensions/uv-av-extension/IAVExtensionData.ts
@@ -1,3 +1,4 @@
 import { IUVData } from "../../../../IUVData";
+import { Config } from "./config/Config";
 
-export interface IAVExtensionData extends IUVData {}
+export interface IAVExtensionData extends IUVData<Config> {}
diff --git a/src/content-handlers/iiif/extensions/uv-default-extension/Extension.ts b/src/content-handlers/iiif/extensions/uv-default-extension/Extension.ts
index 434c9b681..119dc3181 100644
--- a/src/content-handlers/iiif/extensions/uv-default-extension/Extension.ts
+++ b/src/content-handlers/iiif/extensions/uv-default-extension/Extension.ts
@@ -14,7 +14,7 @@ import "./theme/theme.less";
 import defaultConfig from "./config/config.json";
 import { Config } from "./config/Config";
 
-export default class Extension extends BaseExtension
+export default class Extension extends BaseExtension<Config>
   implements IDefaultExtension {
   $downloadDialogue: JQuery;
   $shareDialogue: JQuery;
diff --git a/src/content-handlers/iiif/extensions/uv-ebook-extension/Extension.ts b/src/content-handlers/iiif/extensions/uv-ebook-extension/Extension.ts
index 7ed357bff..7b4d32c80 100644
--- a/src/content-handlers/iiif/extensions/uv-ebook-extension/Extension.ts
+++ b/src/content-handlers/iiif/extensions/uv-ebook-extension/Extension.ts
@@ -18,7 +18,7 @@ import "./theme/theme.less";
 import defaultConfig from "./config/config.json";
 import { Config } from "./config/Config";
 
-export default class Extension extends BaseExtension
+export default class Extension extends BaseExtension<Config>
   implements IEbookExtension {
   $downloadDialogue: JQuery;
   $moreInfoDialogue: JQuery;
diff --git a/src/content-handlers/iiif/extensions/uv-ebook-extension/IEbookExtensionData.ts b/src/content-handlers/iiif/extensions/uv-ebook-extension/IEbookExtensionData.ts
index 8044bcb2e..a9071d9a7 100644
--- a/src/content-handlers/iiif/extensions/uv-ebook-extension/IEbookExtensionData.ts
+++ b/src/content-handlers/iiif/extensions/uv-ebook-extension/IEbookExtensionData.ts
@@ -1,5 +1,6 @@
 import { IUVData } from "../../../../IUVData";
+import { Config } from "./config/Config";
 
-export interface IEbookExtensionData extends IUVData {
+export interface IEbookExtensionData extends IUVData<Config> {
   cfi: string;
 }
diff --git a/src/content-handlers/iiif/extensions/uv-mediaelement-extension/Extension.ts b/src/content-handlers/iiif/extensions/uv-mediaelement-extension/Extension.ts
index d260d85ca..96c5a83c6 100644
--- a/src/content-handlers/iiif/extensions/uv-mediaelement-extension/Extension.ts
+++ b/src/content-handlers/iiif/extensions/uv-mediaelement-extension/Extension.ts
@@ -30,7 +30,7 @@ import defaultConfig from "./config/config.json";
 import { Events } from "../../../../Events";
 import { Config } from "./config/Config";
 
-export default class Extension extends BaseExtension
+export default class Extension extends BaseExtension<Config>
   implements IMediaElementExtension {
   $downloadDialogue: JQuery;
   $shareDialogue: JQuery;
diff --git a/src/content-handlers/iiif/extensions/uv-model-viewer-extension/Extension.ts b/src/content-handlers/iiif/extensions/uv-model-viewer-extension/Extension.ts
index 5daf2f91b..0d202eb6f 100644
--- a/src/content-handlers/iiif/extensions/uv-model-viewer-extension/Extension.ts
+++ b/src/content-handlers/iiif/extensions/uv-model-viewer-extension/Extension.ts
@@ -23,7 +23,7 @@ import { AnnotationGroup } from "@iiif/manifold";
 import { AnnotationResults } from "../../modules/uv-shared-module/AnnotationResults";
 import { Config } from "./config/Config";
 
-export default class ModelViewerExtension extends BaseExtension {
+export default class ModelViewerExtension extends BaseExtension<Config> {
   $downloadDialogue: JQuery;
   $shareDialogue: JQuery;
   $helpDialogue: JQuery;
diff --git a/src/content-handlers/iiif/extensions/uv-openseadragon-extension/Extension.ts b/src/content-handlers/iiif/extensions/uv-openseadragon-extension/Extension.ts
index 699e87a16..a24c6bc1e 100644
--- a/src/content-handlers/iiif/extensions/uv-openseadragon-extension/Extension.ts
+++ b/src/content-handlers/iiif/extensions/uv-openseadragon-extension/Extension.ts
@@ -55,7 +55,7 @@ import { merge } from "../../../../Utils";
 import defaultConfig from "./config/config.json";
 import { Config } from "./config/Config";
 
-export default class OpenSeadragonExtension extends BaseExtension {
+export default class OpenSeadragonExtension extends BaseExtension<Config> {
   $downloadDialogue: JQuery;
   $externalContentDialogue: JQuery;
   $helpDialogue: JQuery;
diff --git a/src/content-handlers/iiif/extensions/uv-pdf-extension/Extension.ts b/src/content-handlers/iiif/extensions/uv-pdf-extension/Extension.ts
index ad08c1871..845ff57f6 100644
--- a/src/content-handlers/iiif/extensions/uv-pdf-extension/Extension.ts
+++ b/src/content-handlers/iiif/extensions/uv-pdf-extension/Extension.ts
@@ -18,7 +18,8 @@ import defaultConfig from "./config/config.json";
 import { Events } from "../../../../Events";
 import { Config } from "./config/Config";
 
-export default class Extension extends BaseExtension implements IPDFExtension {
+export default class Extension extends BaseExtension<Config>
+  implements IPDFExtension {
   $downloadDialogue: JQuery;
   $shareDialogue: JQuery;
   $helpDialogue: JQuery;
diff --git a/src/content-handlers/iiif/extensions/uv-pdf-extension/IPDFExtensionData.ts b/src/content-handlers/iiif/extensions/uv-pdf-extension/IPDFExtensionData.ts
index cf1c4b12a..4ecc425c8 100644
--- a/src/content-handlers/iiif/extensions/uv-pdf-extension/IPDFExtensionData.ts
+++ b/src/content-handlers/iiif/extensions/uv-pdf-extension/IPDFExtensionData.ts
@@ -1,5 +1,6 @@
 import { IUVData } from "../../../../IUVData";
+import { Config } from "./config/Config";
 
-export interface IPDFExtensionData extends IUVData {
+export interface IPDFExtensionData extends IUVData<Config> {
   anchor: string | null;
 }
diff --git a/src/content-handlers/iiif/extensions/uv-pdf-extension/config/Config.ts b/src/content-handlers/iiif/extensions/uv-pdf-extension/config/Config.ts
index 30f142a17..e3aeb9a30 100644
--- a/src/content-handlers/iiif/extensions/uv-pdf-extension/config/Config.ts
+++ b/src/content-handlers/iiif/extensions/uv-pdf-extension/config/Config.ts
@@ -1,7 +1,13 @@
-import { BaseConfig } from "@/content-handlers/iiif/BaseConfig";
+import { BaseConfig, Options } from "@/content-handlers/iiif/BaseConfig";
 
 type Modules = {};
 
+type PDFOptions = Options & {
+  /** Determines if PDF.js should be used for PDF rendering */
+  usePdfJs?: boolean;
+};
+
 export type Config = BaseConfig & {
+  options: PDFOptions;
   modules: Modules;
 };
diff --git a/src/content-handlers/iiif/modules/uv-pdfcenterpanel-module/PDFCenterPanel.ts b/src/content-handlers/iiif/modules/uv-pdfcenterpanel-module/PDFCenterPanel.ts
index b62e55c0d..1e30700ab 100644
--- a/src/content-handlers/iiif/modules/uv-pdfcenterpanel-module/PDFCenterPanel.ts
+++ b/src/content-handlers/iiif/modules/uv-pdfcenterpanel-module/PDFCenterPanel.ts
@@ -6,6 +6,7 @@ import { Bools } from "@edsilv/utils";
 import { AnnotationBody, Canvas, IExternalResource } from "manifesto.js";
 import { Events } from "../../../../Events";
 import { loadScripts } from "../../../../Utils";
+import { Config } from "../../extensions/uv-pdf-extension/config/Config";
 
 // declare var PDFJS: any;
 
@@ -57,7 +58,12 @@ export class PDFCenterPanel extends CenterPanel {
     // Only attach PDF controls if we're using PDF.js; they have no meaning in
     // PDFObject. However, we still create the objects above so that references
     // to them do not cause errors (simpler than putting usePdfJs checks all over):
-    if (Bools.getBool(this.extension.data.config!.options.usePdfJs, false)) {
+    if (
+      Bools.getBool(
+        (this.extension.data.config! as Config).options.usePdfJs,
+        false
+      )
+    ) {
       // this.$content.append(this._$spinner);
       this.$content.append(this._$progress);
       this.$content.append(this._$prevButton);
@@ -265,7 +271,12 @@ export class PDFCenterPanel extends CenterPanel {
 
     this._lastMediaUri = mediaUri;
 
-    if (!Bools.getBool(this.extension.data.config!.options.usePdfJs, false)) {
+    if (
+      !Bools.getBool(
+        (this.extension.data.config! as Config).options.usePdfJs,
+        false
+      )
+    ) {
       window.PDFObject = await import(
         /* webpackChunkName: "pdfobject" */ /* webpackMode: "lazy" */ "pdfobject"
       );
@@ -317,7 +328,12 @@ export class PDFCenterPanel extends CenterPanel {
   }
 
   private _render(num: number): void {
-    if (!Bools.getBool(this.extension.data.config!.options.usePdfJs, false)) {
+    if (
+      !Bools.getBool(
+        (this.extension.data.config! as Config).options.usePdfJs,
+        false
+      )
+    ) {
       return;
     }
 
diff --git a/src/content-handlers/iiif/modules/uv-shared-module/BaseExtension.ts b/src/content-handlers/iiif/modules/uv-shared-module/BaseExtension.ts
index bab84dce9..38f77b818 100644
--- a/src/content-handlers/iiif/modules/uv-shared-module/BaseExtension.ts
+++ b/src/content-handlers/iiif/modules/uv-shared-module/BaseExtension.ts
@@ -49,7 +49,7 @@ import { StoreApi } from "zustand/vanilla";
 import { ExtensionState } from "./ExtensionState";
 import { BaseConfig, Metric, MetricType } from "../../BaseConfig";
 
-export class BaseExtension implements IExtension {
+export class BaseExtension<T extends BaseConfig> implements IExtension {
   $authDialogue: JQuery;
   $clickThroughDialogue: JQuery;
   $element: JQuery;
@@ -59,7 +59,7 @@ export class BaseExtension implements IExtension {
   annotations: AnnotationGroup[] = [];
   clickThroughDialogue: ClickThroughDialogue;
   extensionHost: IIIFExtensionHost;
-  data: IUVData;
+  data: IUVData<T>;
   extensions: any;
   helper: Helper;
   isCreated: boolean = false;
@@ -79,7 +79,7 @@ export class BaseExtension implements IExtension {
   tabbing: boolean = false;
   browserDetect: BrowserDetect;
   locales = {};
-  defaultConfig: BaseConfig;
+  defaultConfig: T;
 
   public create(): void {
     const that = this;
@@ -181,7 +181,7 @@ export class BaseExtension implements IExtension {
 
           if (manifestUri) {
             this.fire(Events.DROP, manifestUri);
-            const data: IUVData = <IUVData>{};
+            const data: IUVData<T> = <IUVData<T>>{};
             data.iiifManifestId = manifestUri;
             this.reload(data);
           }
@@ -714,7 +714,7 @@ export class BaseExtension implements IExtension {
   }
 
   // re-bootstraps the application with new querystring params
-  reload(data?: IUVData): void {
+  reload(data?: IUVData<T>): void {
     this.extensionHost.publish(Events.RELOAD, data);
   }
 
@@ -1039,7 +1039,7 @@ export class BaseExtension implements IExtension {
 
   // todo: use redux in manifold to get reset state
   viewManifest(manifest: Manifest): void {
-    const data: IUVData = <IUVData>{};
+    const data: IUVData<T> = <IUVData<T>>{};
     data.iiifManifestId = this.helper.manifestUri;
     data.collectionIndex = <number>this.helper.getCollectionIndex(manifest);
     data.manifestIndex = <number>manifest.index;
@@ -1050,7 +1050,7 @@ export class BaseExtension implements IExtension {
 
   // todo: use redux in manifold to get reset state
   viewCollection(collection: Collection): void {
-    const data: IUVData = <IUVData>{};
+    const data: IUVData<T> = <IUVData<T>>{};
     //data.manifestUri = this.helper.manifestUri;
     data.iiifManifestId = collection.parentCollection
       ? collection.parentCollection.id
@@ -1168,7 +1168,7 @@ export class BaseExtension implements IExtension {
 
   changeLocale(locale: string): void {
     // re-order locales so the passed locale is first
-    const data: IUVData = <IUVData>{};
+    const data: IUVData<T> = <IUVData<T>>{};
 
     if (this.data.locales) {
       data.locales = this.data.locales.slice(0);
diff --git a/src/content-handlers/iiif/modules/uv-shared-module/IExtension.ts b/src/content-handlers/iiif/modules/uv-shared-module/IExtension.ts
index 219c68cf5..0812ae480 100644
--- a/src/content-handlers/iiif/modules/uv-shared-module/IExtension.ts
+++ b/src/content-handlers/iiif/modules/uv-shared-module/IExtension.ts
@@ -27,7 +27,7 @@ export interface IExtension {
   extensionHost: IIIFExtensionHost;
   create(): void;
   createModules(): void;
-  data: IUVData;
+  data: IUVData<BaseConfig>;
   defaultConfig: BaseConfig;
   dispose(): void;
   exitFullScreen(): void;
@@ -71,7 +71,7 @@ export interface IExtension {
   type: ExtensionLoader;
   redirect(uri: string): void;
   refresh(): void;
-  reload(data?: IUVData): void;
+  reload(data?: IUVData<BaseConfig>): void;
   resize(): void;
   resources: IExternalResourceData[] | null;
   shifted: boolean;