Yep, it’s out. I’m posting with it (on Linux) right now.
Looks faster, and so far hasn’t crashed yet, except when I opened the file browser: it crashed every time, then. But I was using development (2.7.x) versions of GTK, compiled a month or so ago; since 2.8.3 is out, which is a stable version, I compiled and installed it, and presto! Problem solved!
(to those who say “see, Linux is too complicated, some library versions make programs crash, and you have to compile stuff”, I was using the development libraries because I wanted to! I didn’t need them for anything in particular, and I could have stayed with RPM versions, but I’m a “bleeding edge” maniac (less so than years ago, but still a bit :)).
EDIT: It’s not “faster”, it’s way faster. It’s when you browse familiar pages and you are, unconsciously, expecting them to take a little time to draw themselves, and they appear instantly, that you notice it. I recommend you try it. 
I’ll install it on my home Windows PC later today, too.
EDIT #2: Using it on my XP home PC as well. Zero crashes, zero problems so far. Also, in less than 24 hours, I’ve found that about half of the extensions I use have been updated and are now compatible. I’d guess that most or all of them will be, in a day or two.
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Something where I note a big difference is when opening several pages on different tabs. On Firefox 1.0.x, the UI would become momentarily unusable while some heavier page was loading and rendering (even if its was in background). Already knew that this would be solved for Firefox 1.1 (which, meanwhile, turned out to be 1.5), and so it is!
I only find something rather annoying, which I didn’t think happened before: when you open a full bookmarks folder with middle-click (=each page on that folder in a tab), FF 1.5b1 completely nukes any tabs that were open before — whereas (if I can recall) FF 1.0.x added the bookmarks’ tabs to the already open ones.
João:
- Open about:config
- look for browser.tabs.loadFolderAndReplace
- change to “false”
Problem solved.
One other thing: the speed when you browse back (either by clicking on the “Back” button or by pressing BackSpace) is… well, it’s instantaneous.
Well, I came back exactly to ammed what I said, but it isn’t related to that configuration (at least directly). I now installed a 1.5-compatible version of Tabbrowser Preferences, and I have the desired behaviour.
Yep. It is way faster overall: app loading, page loading, UI, …
Linux is too complicated
! I don’t like 1.5b1, none of my extensions work, and the feeds been at the top is just a pain! I don’t like the new skin either. It is faster though 
BA~~9
I started using it as well, this is much better than ie in windows. I no longer have the stability issues
@Joe Anderson’s “I don’t like 1.5b1, none of my extensions work”
Well, evolution has a price — which you have also paid when Windows XP came around; did you also “not like it because program A didn’t work or hardware part B lacked drivers”?
You may not see the importance now, but this was the first time someone (other than me) commented on someone else’s comment, in this blog. Took almost 2 weeks.
As for extensions, I believe almost all of them will be updated in less than a week. Some have already been, in the past couple of hours.