Opera.
I used opera from the start. Once my classmate told me firefox owns opera, so I wanted to find out how much it owns so I installed it and started using for everyday tasks.
1 month later, I was sick of it.
The reasons sumed up are:
Firefox deleted my bookmarks 3 times,
6 times I had to find/install all the extensions because they refused to work and I don't know the reason why.
About 60% of all my downloads crashing firefox at the end.
None of the skins look good.
Most of the extensions you will download are opera-like feature addons.
The tabbed browsing never works as i want it to work.
Did a little test the other day. I executed firefox(10extensions and 2 skins no tabs open) and untill it actualy loaded 100%, I managed to open and close opera with 69 tabs open 3 TIMES!
Oh and, everyone knows firefox has some HUGE issues with the performance:
Websites load faster (A LOT FASTER) with opera, not even cached ones.
Try looking at a gif file with more than 1 frame in firefox and look at task manager. It uses most of the cpu while rendering the gif file, while opera does that with ease. And dont think my PC Specs are low, I play hl2 on everything high, full AA and AF 1240x1024 on average of 70 FPS.
So, the thing i noticed about firefox or ie users, is that they judge about other browsers without even trying it properly (like I was trying to see ANYTHING good about firefox the whole month).
So, before you think your browser is the best of all, try others!