I've developed a few browser extensions, and every week I receive numerous emails with "revenue offer". Some experienced developers know that offers like these will inject malware into the browsers of your users, but scammers who make these offers will not tell you about it. They offer "integrations" that don't look so suspicious. Imagine how many developers have accepted these offers. Then look at the number of extensions in your browser and think about how much risk there is that you have an extension with malware.
To be specific: from trusted developers. Installing them only from the official repository (is it still possible to reasonably install them any other way?) won’t help if a dev sells such an addon. On the other hand I cannot imagine someone like Raymond Hill (the uBlock Origin dev) doing it, considering his track record.
Yeah, that’s what I meant.