Okay to get XP with all your updates. Get AutoPatcher. From there unzip it ot a folder. Google for nlite and use that to create your own custom install XP disc with all the current updates.
The other part where you want all your apps. Will never happen. Cause of the fact that all the installs run differently and you can not run them upon a XP install. They need XP to be isntalled first. So your only option there is to isntall Acronis or Norton Ghost. From there you can just make a Image of your drive and have everything the way you want it everytime. Only problem with that is when new updates are released you will have to download them all the time you use this image.
As for you firfox issue. Simple solution. Open My Computer. Click on Tools>Folder Options>View>Show hidden files and folders. Now go into Doc&Settings>USerName>App Data>Mozilla>Firefox ( I think that is the correct path. It should bevery similar to this) Save that folder to a External drive or whatever you wish. After you do a install just copy this folder back everytime to the same location you found it. All settings, extensions, bookmarks should all be there jsut like they were. I do this all the time with my Opera settings.
I hope i helped shine some light on the issues you are looking at.