That is not the case. Chrome's API is just a base. The proposal is to be able to handle most of Firefox's add-on ecosystem IIRC. The code would have to change,

That is not the case. Chrome's API is just a base. The proposal is to be able to handle most of Firefox's add-on ecosystem IIRC. The code would have to change, but the functionality would be the same. There is a lot of misinformation out there about Firefox's switch to web extensions. Existing add-ons aren't going to be obsoleted immediately ; rather new apis will be added first, and then they will be asked to switch. Currently Firefox add-ons often hook directly into the browser, which is hard to keep secure and makes it hard to evolve the browser.