>My personal sense is that browser extensions in general are a technology that's on the far side of the adoption bell curve. As the Web itself becomes a more capable platform, many scenarios that used to require an extension can now be handled quite well by sites on their own.
I disagree. Many kinds of extensions are designed to work across multiple sites, and add functionality most websites would either be unwilling or uninterested in adding. Consider extensions like Ad Blockers, Privacy Extensions preventing tracking, HTTPS Everywhere, No Script, download managers, extensions which affect the browser display as a whole (such as Tree Style Tabs), etc.
True, but (1) for better or worse, these are all things that are of interest primarily to the clued-in nerd audience, not the public at large; and (2) the greater capabilities offered to extensions are a double-edged sword. It's true that extensions can do things that sites cannot, but that also means that they can compromise users' security and privacy in ways sites cannot too. In a world that's a lot more security-conscious than it was 15 years ago, a decent argument can be made that the security risks highly empowered extensions present outweigh the value they bring to the table. (That's a decision that ultimately rests on how popular they are with the mass audience, too; it's easier to shut down a security hole that nobody depends on than one that millions of people do.)
…which is why the add-on review process is time consuming, and why AMO shows you half a dozen warnings before letting you install an unreviewed add-on.
Right -- which is (part of) why interest in extensions is declining. It's a self-reinforcing pattern: platform vendors tighten security on extensions; extensions can now do less and are harder to get, so fewer people try them; which makes it easier to tighten the security screws on extensions the next time around.
I disagree. Many kinds of extensions are designed to work across multiple sites, and add functionality most websites would either be unwilling or uninterested in adding. Consider extensions like Ad Blockers, Privacy Extensions preventing tracking, HTTPS Everywhere, No Script, download managers, extensions which affect the browser display as a whole (such as Tree Style Tabs), etc.