Add support for Firefox on Android

[ErikBjare]

A major gap in my personal logging is that all browsing on my phone just gets logged as "Firefox" by SmarterTime. It would be nice to remedy that. We might be able to get sync by using the storage.synced space on both a phone and a desktop.

[lidorcg]

I wrote an extension with the exact same goal and tried to use the sync storage for synchronization but was unable to get it to work. Eventually had to settle for centrelized solution...

[adminvulcano]

Firefox now supports all extensions on android (announcement)! Because ActivityWatch is not explicitly marked as supporting Android, it is only available in the store when forcing the desktop page, but from there, it installs fine. However, after installing the extension, I cannot accept the privacy policy as the corresponding window does not show when pressing "Consent to Privacy Notice" in the extension settings. This page likely has more information why that is, but I am not familiar enough with the code to find a fix. Would be really great if the extension worked, this would close a big gap in my tracking too!