Firefox 3.6.15, mostly because I don't want to go through the process of
figuring out which add-ons are now broken and how to fix or replace them
like I have to do with every major release of Firefox. Chrome never
interested me, and I really don't want to spend a bunch of time looking
for add-ons that may not exist. I'm down to 59 extensions (this will
likely go down again since I'll prune in process of moving to Fx 4), and
replacing them is a daunting task I'd rather not take when there's
really no compelling reason to switch to Chrome (except the tabs as
processes feature, but sessions are saved automatically by Tab Mix
Plus). BTW, if you think 59 is a lot, I was up to around 100 when the
latest Firefox was 3.0.x. Over time, extensions can break (either on
their own or with a major change to Gecko), are unneeded, or are
unnecessary when their functionality is built into Firefox, so that
number will steadily decrease.