Default to last Firefox install if multiple

When _not_ explicitly requesting a specific Firefox profile directory
the default profile is chosen. However on top of profiles Firefox may
have multiple "installs" (listed in the `installs.ini` file) each with
their own default profile.

Before, the default profile was the one from the first install.
However, it makes more sense to pick the last one instead, assuming
that that's the most recently created one, and thus the active one.

Author: DukeSliver

src/pycookiecheat/firefox.py

@@ -107,8 +107,8 @@ def _find_firefox_default_profile(firefox_dir: Path) -> str:
     profiles_ini.read(firefox_dir / "profiles.ini")
     installs = [s for s in profiles_ini.sections() if s.startswith("Install")]
     if installs:  # Firefox >= 67
-        # Heuristic: Take the first install, that's probably the system install
-        return profiles_ini[installs[0]]["Default"]
+        # Heuristic: Take the most recently created profile which should be the active one.
+        return profiles_ini[installs[-1]]["Default"]
     else:  # Firefox < 67
         profiles = [
             s for s in profiles_ini.sections() if s.startswith("Profile")