Using all three... FF, Chrome and IE. (IE in some oddball cases esp virtual server 2005 and other web sites that still doesn't play ball with FF and Chrome).
Most of us have one...and only one. Sometimes a few of us get lucky and have TWO at a time, but as good as it sounds it's just too difficult to maintain two, at the same time.
Too many conflicts.. one will ask to be the main one, you say "yes" and when you go to the other one, that one will want to be the "primary" one!
Then there is people like you who are only satisfied with three, and nothing less. Most of us couldn't even handle that amount of button pressing and wheel flicking in a scenario like that, it just ain't practical. Not for one man. 3 requires just too much Ram Power, and a lot of virtual swapping per session.
I'm guessing there is some freak here who probably likes to have 4 at a time, but that's just crazy talk.
No man can sustain that kind of cache requirements - and even if you could, your cache would run out very quickly.
Sure you get cookies like crazy, and yes the plug-in possibilities are endless - but it just ain't worth it. Unless you have a big hard drive of course.