Why there are so few browser extensions developed by npapi?

Question

I want to develop extensions for some main browsers like chrome and firefox. Extensions written using npapi can work in different browsers, however, there are very few browser extensions developed with npapi. Can you tell me the reasons? Thank you.

Answer 1

Your question confuses extensions and plugins; they are very different, and have completely different goals. You cannot develop an extension using NPAPI, only a plugin. You cannot write a single extension that works across browsers.

If you are asking why very few extensions include plugins, it's because plugins are much harder to write than extensions, are platform-specific, are not necessary for the vast majority of problems that extensions are trying to solve, are much more dangerous to users (since they have access to run arbitrary code on the machine), and aren't even allowed in extensions in some browsers (e.g., Safari).

If you didn't mean extensions at all, and are asking why there are few stand-alone NPAPI plugins, most of the list above still applies.