Firefox lives by its extensions

I've been running 4.0 beta as my main browser since it came out, and haven't noticed any crashes or major bugs.

I don't know about synthetic benchmarks, but browsing with AdBlock and NoScript is noticeably faster than browsing in Chrome or Opera, which don't have equivalent functionality.

No, they really don't - unless scripts can be allowed or blocked on a per-domain basis within the same page (so you can could to allow theregister.co.uk, but disallow googleadservices.com and quantserve.com), and without script surrogate functionality, you're stuck with a binary choice of either allowing or disallowing script for a site. So unless you can disallow all script for the entire site (not usually very nice), you gain no performance benefit.

The AdBlock 'substitutes' I've seen don't have anything approaching the filter list subscription and easy element selection for blocking functionality, some don't collapse the blocked elements (so even if the ad isn't present, you still get a big blank spot intruding), some download the ad even if not displayed (negating performance benefits) and so on.

Bare Firefox without extensions may be arguably not as good as bare Chrome or Opera - I personally still prefer using it, but would concede that other browsers have advantages too. With extensions in the mix, though, nothing can touch Firefox.

I tried it

I tried it an can't figure out why they put the tabs way up in the middle of the everything instead of right above the page which is the natural place to put them.

I think I'll stick with the last version of 3 till they either move them back to where they were in 3.x or till I find a replacement that has them right above the window. Can't figure out why they decided to change it, if it isn't broke don't fix it.