[RunningDroid]

If you modify the AppConstants file (inside omni.ja) you can install unsigned extensions anyway:

https://gist.github.com/TheBrokenRail/c43bf0f07f4860adac2631...

[yjftsjthsd-h]

That link appears to describe a process for patching the Firefox package. That does not strike me as a reasonable solution.

[RunningDroid]

I didn't say it was reasonable, just that it's an option.