3 points
Isn’t that already how it works? Are there extensions trust work unchanged on both browsers? At the very least they’d have to maintain them on both addon stores.
There’s a common specification called WebExtension, which is used by all modern browsers. Firefox had their own API (XUL/XPCOM) before that, but they deprecated it in 2017. Safari also used to have its own system for extensions, but it’s been deprecated since 2019. The Manifest API is a subset of WebExtension, which defines an extension.
