I have to admit the only real reason I'm on FF is tree style tabs. All the tabs on the left of the screen, with little markers to expand or minimize the tree. No tabs along the top (needs a tiny bit of css), plus I can customize the look. I tried to get Chrome to do this but nothing was satisfying.

Now it's not like FF is inferior in all other ways, it is actually a pretty good experience. But TST is the big one for me, can't live without it.