It is semantics that plagues you and I.
I don't think something is "usable" unless it works like the user wants it to work. You feel it is "usable" if you can use like it comes even though you dislike a great deal about the way it is out of the box. That's a semantics disagreement about what the word "usable" means. We are both right or both wrong as the answer is based on how a person defines "usable".
My extensions work fine. But there is no Spellbound extension for Fx3 and I cannot turn off the spell checker even though the box to use it in Options/advanced is unchecked. I also cannot turn it off on the Vista machine. I have to right click uncheck the "check spelling" box every time I go to make a post. Then when I preview the post and want to change something, add something, the spell checker has been turned back on. It is awful. It is like a leech that cannot be dislodged. The new TBE extensions are ok but the auto hide doesn't work right and I had to turn that off. I have three extensions where I have one for 1.5. I have the awesome bar fixed and I don't have to hassle with getting rid of the favicons like my friend just did and sent me the rather convoluted fix because I installed CookieSafe and it now, with the latest version, blocks all those myriad of third party favicon cookies.
I don't understand your comment about IE and downloads. IE downloads are dangerous because IE does not stop you from running the download. Fx is far superior in this regard so there is no need for Fx to go begging to IE about some Windows standards that Microsoft doesn't even have. As for the anti virus being hijacked by Fx3, of course, I turned that off. Why would you think I wouldn't? I had not encountered the behavior because I don't run AV on my virtual machines...(well, I will be running one on the Vista one because it is the inferior Microsoft Virtual PC which has no ability to take snapshots or clone).
Where did you get the idea that Fx cannot run on virtual machines? If true, that would set Fx back eons. I fired up my virtual machine that has Fx2 on it and it loads all sites rapidly. There is no problem with VMWare. It's something with Fx3. As I said, I have done a great deal of "tweaking" as you call it ...I call the same thing making the browser "usable" and probably something I did borked it. I have IE 8 on that machine and it has lots of problems so trying it to see if it could be something with that XP Pro install (rather than Fx2) isn't much help. I don't think I installed Opera on that machine. The virtual machines have a fixed size hard drive which is small so I can't put a lot on them. That is one nice thing about MS Virtual PC..I can change the size of the hard drive on the fly or add more hard drives if I want.--
"The same ferocity that our founders devoted to protect the freedom and independence of the press is now appropriate for our defense of the freedom of the internet. The stakes are the same: the survival of our Republic". Al Gore, The Assault on Reason