Firefox is already running but not running in reality problem

These days, I have strange problem with my Firefox. When I run Firefox and do the job without any problem. As soon as I close the Firefox and re-open or run, it says "Firefox is already running, but is not responding. To open a new window, you must first close the existing Firefox process, or restart your system." like in the picture. I am not sure whether it is due to virus, spam or hardware failure.

I tried to solve the problem as per the suggestions found in internet but they worked just for once. Hence if you have any suggestions besides deleting parent.lock file or whole profile file or changing the profile folder from read only to read/write..., please help.