Why should anyone laugh? There are all levels of computer users out there. Unfamiliarity is nothing to be ashamed of.
As for Firefox 3, I've also gotten the notifications, but turned them off by clicking the "Never" option as far as future notifications. I'll decide when/why I want to upgrade.
Version 3 is new, so reasonable evaluations may be awhile. If you're not upset with what version of Firefox you have, I'd simply continue with it for now.
Go for it!
And no, it shouldn't do anything to XP. Now what XP might do to it, I can't say as I run Linux. And BTW: There's absolutely nothing wrong with asking questions.
Thanks. My present Firefox is fine.