It’s out. Go download it. I just did, for Windows; I’ll only try the Linux version when I get back to slaving thanklessly to please my overseers… uh… to work. 
Just like I said for the first beta: it doesn’t look like “beta” at all; I’d guess it’s more stable than 1.0.x. Some extensions haven’t been updated yet (the authors are probably asleep :)) but I expect them to be (updated, not asleep) quickly, like they were before.
If you’re in a hurry, you can simply download the .xpi file for a still not updated extension, uncompress it (they’re .zip files, actually), edit the install.rdf file with a text editor, and change the “maximum version” to 1.4.1 (or 1.5, to handle any next betas), then recreate the .xpi file (zipping its contents, now with the altered file) again, and open it in Firefox. There you go, a compatible extension.
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On the previous versions of firefox 0.9 and 1.0, I had a few problems with some extensions, because they were “made” for a particular version and therefore, wouldn’t run well on another version than the specific one(s).
The only way to try the extension on another version, was by altering the [i]app.version[/i] on the [u]about:config[/u] window.
That is, in comparison with your suggestion, we could say that “if Maomé doesn’t go to the mountain, the mountain goes to Maomé”…
Instead of altering the .xpi file, we altered firefox, temporarily ofcourse, because after the installation I turned the app.version, back to normal.
I haven’t tried yet any of the beta versions, but I’m thinking on it…