Firefox recently deprecated their entire legacy extension system, in favour of a new, more secure system based on Chrome's extension system, and also on the W3C

Firefox recently deprecated their entire legacy extension system, in favour of a new, more secure system based on Chrome's extension system, and also on the W3C's draft spec[0] This means that many things should be identical between them: including but not limited to the packaging format, manifest format, security model, and the basic APIs for simple common browser features like tabs, page loads, network connections, etc. which gives you a very high compatibility surface area. Naturally, APIs for any innovative features either browser have will be unique to that browser. e.g. Firefox has unique APIs for it's Container system, and it's Sidebar. I guess Chrome has some unique features too. [0] https://browserext.github.io/browserext/ https://browserext.github.io/browserext/