I've known about, and have been using, Firefox for about 3 months (I've shied away from previous mozilla versions for compatibility issues, etc...). Firefox is nice and all, but it's tabbed browsing was fundementally flawed....
See, If I'm going to have multiple tabs, I wanted ALL my new windows to open up in tabs, not new window iterations. The automatic new window calls would still create multiple firefox instances and drove me up the wall.
So I went back to IE (where it's a given) and Slimbrowser (and IE shell), which did tabbing right.
I've consistantly checked for tab browsing extension and hadn't found any that addressed my concern ... until now. Tabbrowser Preferences
check it out... best ever.
[ I didn't add to the original firefox post ... it's too bloated to revive. This is just a recommendation for a specific extension ]