It does seem to be improved, but on my system (new-ish MBP running OS X), Chrome and Safari startup is nearly instantaneous, and Firefox still lags. I don't know how it compares on Windows.
Still.. bravo to the Firefox team for making a big improvement in this department. My ire is now refocused on the (lack of) JavaScript performance. :-)
Do you have a lot of plugins installed? I tested on a 6-month-old MacBook Pro 13", on both OS X and Win7, and Firefox starts up pretty much instantly (less than 500msecs). Agreed, Chrome and Safari seem marginally faster, but I don't close my browser very often, so it really doesn't matter.
Still.. bravo to the Firefox team for making a big improvement in this department. My ire is now refocused on the (lack of) JavaScript performance. :-)