BleepingComputer.com: cannot open firefox

I am running XP Pro on my desk computer and using firefox browser for more than five years with no problem.
Today I found out a very annoying problem:
When I am opening the browser everything work smooth, but if I want to open a second one (when the first one is still open) to browse separately , the browser is not responding. I can click on the firefox icon with no reaction. I have only one tab open
If I exit firefox (close the open tab) I cannot reopen the browser . In order to open it again , I have to restart the PC.
I uninstall the program and reinstall it again, but above issue remain.
I cleared the ProfileManager and reinstalled the program , same issue.

Need assistance. Thanks