It does, but it's nowhere near as smooth, and I'm not talking about dialogs and user intervention.
Whereas Chrome has a stable extension API, Firefox really breaks at least one very popular plugin withe each "release." So then you get nasty warnings about incompatible plugin versions and whether or not you want to look up a new version of the plugin. Whereas Chrome a) doesn't break plugin APIs very often, even in alpha and beta channels and b) automatically updates plugins anyway.
Firefox also upgrades plugins automatically, provided they pass a bunch of automated tests. Unfortunately, it seems many don't.
The openness of their API is certainly a two edge sword; in one way, it lets developers dig deep in the browser's internals, which means addons can be immensely more powerful than on Chrome; on the other hand, it means they have a dependency on those same internal APIs.
They've launched the Jetpack SDK as a stable API for addons that doesn't require browser restarts to install them, but almost no one uses it:|
I wonder if there's anything other than momentum holding Jetpack back. I would be interested in trying to get some add-ons ported just for fun. I do agree that the add-ons in Firefox are way more powerful; I like that Adblock on FF can block ads before they're even retrieved (leaving my Hulu experience punctuated by silence rather than noise).
> It's not really the API which breaks, it's the versioning.
It is definitely the API which breaks in many cases. These 6-week updates change APIs, both Web APIs (used by both websites and addons) and internal APIs.
For example, websites - not addons - can and do break with Firefox and Chrome 6-week updates, because even Web APIs are changed in these rapid updates.
It is true that versioning is a problem as well, however.
Firefox has been forced to follow Chrome on this AFAIK because otherwise some website features (popular ones.. specially GDocs) wouldn't work optimally. Even right now, loading Google sites is faster (specially GMail) on Chrome because only Chrome has SPDY support (coming in a Firefox near you in some weeks thanks to the fast release mechanism!)
The Web APIs aren't stable at many levels, and HTML5 ain't standard. It's a bunch of drafts and some are even conflicting (hello audio APIs).
It seems to me that Google is the main company right now pushing in new drafts and protocols - using it to make other browsers incompatible. Generally the drafts are technically fine and good, the issue is the way they're used to kill diversity and obtain complete web (or "internet") control.
You can start to see a lot of "you need Chrome to see this website. Chrome, the fastest browser on earth by Google! <click to download>.
Specially true if you use Opera or IE which do not update as often as Firefox and Chrome.
Firefox does have a new versionless API, called the bootstrap API. It also allows extensions to stop, start and hence update, without restarting firefox.
Whereas Chrome has a stable extension API, Firefox really breaks at least one very popular plugin withe each "release." So then you get nasty warnings about incompatible plugin versions and whether or not you want to look up a new version of the plugin. Whereas Chrome a) doesn't break plugin APIs very often, even in alpha and beta channels and b) automatically updates plugins anyway.