Just updated to v5.0 and now when I start Firefox I get a pop-up that says checking compatability of add ons and the the Welcome to Firefox page and my home page appears. Can't get rid of the pop up or welcome page.

Question

Above question covers it. I've tried reinstalling Firefox, clearing cache, history, etc. but still happens. I've created app tabs and when I restart Firefox, they are gone. Running Windows XP.

Answer 1

It is probably because you are not properly closing Firefox. Restarting your system would make sure that Firefox had terminated, but you do not have to do that.
To properly close Firefox on Windows systems, use
:File > Exit or "Firefox:" button > Exit
When you get the message "Firefox is already running" it is too late, and you must force termination of Firefox through the Windows Task Manager before restarting Firefox. Windows 7 has a keyboard shortcut to save you a step "Ctrl+Shift+Esc" then on "Processes" tab, select "firefox.exe" and use the "End Process" button. More thorough would be to right-click on the "firefox.exec" and choose "End Process Tree".
You would find firefox.exe in a Mozilla folder in your program files, but y0u would not want to delete it there, you would need to use the Control Panel which you have already identified and do it from there -- but generally you would not need to do that, and there is nothing in what you have posted to indicate that you should. But if you did do that, then don't let the install start Firefox for you as you would want to use you existing desktop icon or method of starting Firefox, and should decline having Firefox install start Firefox for you. When the install starts then invoke Firefox in your normal manner. This should eliminate problems of creating a new profile rather than using your old profile.