I wonder how NEW open source project are still hosted on MS GitHub. I mean, yes, legacy projects hosted there are fine (but should work on leaving Microsoft behind) but new projects? Someone using MS GitHub doesn’t really understand the open source culture. Same with Discord (which is neither a support platform, nor a bugtracker, nor a help articles resource).
There are also projects like qutebrowser which allow external programs to be plugins. In case of qutebrowser it uses the Chromium open source platform as rendering engine, etc. but completely relies on external Python scripts for plugins (including ad blocking).
If Firefox goes down the Chrome route with their forced advertisement I can totally see something like this happening.