Agreed, I would never consider using another browser unless they had vertical tabs. My Firefox typically crashes once per day but treestyle tabs make it worth it.
Once a day? Any idea why? For a while, mine was due to memory issues but they did some seriously awesome work fixing it somewhere in the high teen updates, ever since then it's been solid.
I had the same problem - tree style tabs would make the browser crash constantly. I eventually gave up.
You can make your tabs vertical in Opera without even having to install an extension, though they don't indent like they do in TreeStyleTabs.
The new Opera (using Chrome) lacks vertical tabs unfortunately. Can't seem to find any info on whether it'll come back