For each tab you saved FF has to open a new instance and connect to each site. Same with Exp, though FF is slower. Browser add-ons shouldn't make much diff in loading time, but many of them check for updates, which delays things a bit.

Any reason why I should check out TBird or Safari? Used to use Opera but haven't checked it out since the Change. (They once gave me Opera Pro after I sent them a happy birthday e-mail.)