Firefox is quickly becoming much better than IE. The only thing I don't like is that it makes editing templates harder on vbulletin because the search in individual template function only works in IE.
I also use the bbcode extension. Although I haven't tried it out much, I've used the Paste Quote part of it a little bit more.
I think that Mozilla is okay, and I don't see any errors or problems with displaying any pages. The webmasters on the sites I visit are smart enough to use standard design methods, so it works on Firefox (such as all vB sites that aren't heavily modded).
The only thing I don't like is that it makes editing templates harder on vbulletin because the search in individual template function only works in IE.
I often just copy the text into textpad, then search. Also just because <textarea> fields don't have tabbing capabilities. :'( I wonder if there is a compliant Mozilla and IE wa to do this. IE can do it: http://aspalliance.com/346 :\