The events need to be converted to support event pages. See bug 1815310 for more detail.

Relevant implementation details at https://bugzilla.mozilla.org/show_bug.cgi?id=1796183#c3

In particular:

... need to be updated to account for the possibility of being suspended:

• https://searchfox.org/mozilla-central/rev/e35e7107299a46a696b8aa8a4a5c03a39458ac21/mobile/android/components/extensions/ext-downloads.js#149

Here are examples of how the desktop implementations were updated (plus unit tests):

• ...
• https://hg.mozilla.org/mozilla-central/rev/784ea5bca99393f66217c4e5cf50e9d9acf263b6 (downloads API).

The new unit test here was disabled on Android because the downloads API internals differ for desktop and Android. Android's GeckoView side does have an implementation of downloads (bug 1656336), but lacks integration in A-C and/or Fenix (bug 1538348).

The conversion itself is trivial, so it could be a good exercise in running extension tests and making small changes there. The testing of the downloads API would be much more involved, but if you're experienced with GV development it should be feasible to mock the download internals (via DownloadDelegate; see patches from bug 1656336), either as a xpcshell test or a mochitest

Marking as P3 instead of P2 because the downloads API is not even working yet in Fenix (GeckoView has parts, but A-C/Fenix is not hooked up).