Czuch Chuckers: I would also suggest trying to download the newest copy of firefox if you do not already have the newest version.

No, you should not lose any bookmarks. Some extensions only work for certain versions, but if I remember correctly, it will tell you if it does not work and will go search for newer versions of the extensions for you. (not 100% sure about that.)

Also, you can be safe and export your bookmarks first if you want to make sure you don't lose them. (in firefox, tools, bookmark manager - file, export - into bookmarks.htm - then if you need to, you can import them back - but again, they should copy over automaticly.)

Also, the newest version of firefox will keep itself updated, that is automaticly check for updates and give you options to update it when needed - which is always a good thing for a browser because new security issues for most browsers show up all the time.