Tried Firebird and I have to say that it has all of the features I loved about opera and much more (via extensions... which are much like modules on LS or plugins on MirandaIM (my favorite IM program)... The engine is great, you can have mouse gestures ("all in one gestures" extension), customized search i.e type "g litestep" and search for LS on google, "m hulk" and search imdb for hulk, and whatever search engine you want to add. You can also have tab browsing (which I don't use), and a great popup incorporated blocker. It's a lot more customizable than Opera. You can change some 'deep' settings via some text file editting (user.js, and other) that is familiar to all us "LS fans" here ;)... and much more. Here is a little page on 'why to change to mozilla'.

Has some little bugs (that are worked on on the nightly builds), but even Opera had bugs which they haven't fixed since Opera6.0 (I reported them about 10 times) and BTW Firebird don't have the annoying Opera bugs.

And besides all this it's GNU! and when switching to Linux you can continue using Firebird ;) So definatelly I'm telling Opera good bye, and my vote goes to......

"Mozilla Firebird"