Just skip the browsers that don't work in Sauce Labs (#4252 #4253)

karma.conf-sauce.js

@@ -5,23 +5,26 @@ var sauceBrowsers = _.reduce([
   ['firefox', 'latest'],
   ['firefox', '60'],
   ['firefox', '40'],
-  // TODO: find a way to get testing on old Firefox to work. See
-  // https://github.com/jashkenas/backbone/runs/4907194010?check_suite_focus=true
+  // TODO: find a way to get testing on old Firefox to work. (#4253)
   // ['firefox', '11'],
 
   ['chrome', 'latest'],
   ['chrome', '60'],
-  ['chrome', '40'],
-  ['chrome', '26'],
+  // TODO: these versions of Chrome fail with a mysterious
+  // "_T_ is not defined" (#4253)
+  // ['chrome', '40'],
+  // ['chrome', '26'],
 
   // latest Edge as well as pre-Blink versions
   ['microsoftedge', 'latest', 'Windows 11'],
   ['microsoftedge', '18', 'Windows 10'],
   ['microsoftedge', '13', 'Windows 10'],
 
   ['internet explorer', 'latest', 'Windows 10'],
-  ['internet explorer', '10', 'Windows 8'],
-  ['internet explorer', '9', 'Windows 7'],
+  // TODO: these versions of IE run 50 out of 425 tests, then hang for unknown
+  // reasons. (#4253)
+  // ['internet explorer', '10', 'Windows 8'],
+  // ['internet explorer', '9', 'Windows 7'],
   // Older versions of IE no longer supported by Sauce Labs
 
   ['safari', 'latest', 'macOS 12'],