I'm not exactly sure but check in options in firefox (Tools - Options - Privacy). In here, you can have firefox save your passwords and information. I'm not sure this is what you're asking for. If this isn't it, I would have no idea how to get back into that.
actually this is what i was more looking into , when i log onto my msn messenger and I try to open my email inbox from there , how can i change this so it will open in the firefox browser?