A few days ago, I found a theme in the store that I really liked. However, I didn't like one of the colors and wanted to change it. So, after some searching around, I discovered (from this forum, actually) that you can edit the files for themes and extensions if you use an archive manager or file extraction tool like 7zip. Upon doing this, I was easily able to change the few colors I didn't like and save the theme. I have been using it like this for a few days now, until today I alt+tabbed to Firefox and the theme had been disabled, with a message saying it could not be verified for use and has been disabled. Does anyone know how to fix this, and to keep it from happening in the future? If it helps I am using Manjaro Linux, and the theme was Nord Polar Dark.

EDIT: Turns out the problem was in the "digital signing" of the theme, and when I changed the theme, that signature was no longer valid. If you are using Developer Edition, Nightly, or the Extended Support Release, you can stop this by changing xpinstall.signatures.required to "false" in your about:config. Be warned though, as this means any add-on can now be installed, regardless of whether Mozilla has verified its security.