Can't they just stop making changes that cause plugins and extensions to break?

I know that would be easier said than done, but Chrome seems to do a good job of it.

Firefox addons are traditionally written using the same API the browser itself uses. That's what makes them much more powerful than Chrome extensions, but clearly more fragile to breakage.

They're starting to offer a separate extension SDK (formerly called Jetpack) that allows extensions to ignore the internal API and build against something more stable. Such add-ons can be installed without requiring a restart, and should be much easier to update, but many important extensions need more power than currently provided. (Ad block is a good example.)

As is vimperator and pentadactyl.

In short: Not with the old API. In this recent newsgroup post, you can see a list of the things that could break an extension, and it's a lot.

http://groups.google.com/group/mozilla.dev.planning/browse_t...

The work to solve that is mentioned in the thread.

AFAIK, Chrome plugins still have much less access and power than Firefox plugins, which makes it easier for Chrome.

This is the tail wagging the dog. The plugins are going to be broken whether the update from 3 to 4 happens manually or automatically (and, if anything, discourages manual updating despite all the popups).

Windows has had binary compatibility for decades. Why not just version the internal browser API? (Extension XYZ was built against FireFox 3.6).

>Windows has had binary compatibility for decades.

Extensions don't just run on top of Firefox, though; they modify Firefox's UI in arbitrary ways.

>Why not just version the internal browser API?

Firefox already does this, and automatically disables incompatible extensions.