This has always been the case for years, for every browser. No idea why you say "now". Any browser providing extensions, not just Firefox, will at least won't

This has always been the case for years, for every browser. No idea why you say "now". Any browser providing extensions, not just Firefox, will at least won't allow extensions to modify their own extensions providing page. Otherwise, any malicious extension can infiltrate and trick users to download modified extensions from the browser's own extension page. Comically ignorant.