[cercatrova]

I've written extensions before and Firefox has a very good polyfill [0] that makes it quite easy to write extensions for all browsers. It does get a bit trickier if you also want to incorporate TypeScript [1] or React however.

[0] https://github.com/mozilla/webextension-polyfill

[1] https://github.com/Lusito/webextension-polyfill-ts