The help you have got so far should help you out, but if thats not the case, you may need to dig in to some real system tweaking, which does not just help you to fix the Firefox problem, it will give you more juice out of your laptop, but I will not go deeper into thhat now, it would take hours to but into text
A friend of me got a real old can, Pentium Pro with 200mhz cpu and 128mb mem, I gave it a try, and now it runs WinXP SP2, I admit it took some desent amount of time but evrything is possible
Best Regards
herronk