Important fixes, so don't dawdle. Go to the "Help" menu, and select the item "Install Updates" (they're almost certainly already downloaded). Firefox will have to restart itself, but you'll get all your tabs back and everything. Note that you don't have to reboot your computer or anything.
You may see "Check for Updates" instead of the install option. This means you probably already have the patches, but it can't hurt to check.
Painless, almost completely automatic - that's a security model I can get behind.
And for those of you who run Internet Explorer, you need to read this. Really. IE 8 is a lot better, but it still have ActiveX (security nightmare #1), it has a slower update model (security nightmare #2), and it's still IE, so there's tons of legacy code that the Bad Guys are targeting. Firefox is no panacea, but you win on all three of these fronts.