Firefox doesn't work after three or four usages

[Jayhawker]

Please, is there any way to solve Firefox last-version denying to open after three or four usages. Then, when clicking, a warns appears saying "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".

Please, is there any way to solve it without restarting the system? That's to say any way to "close the existing Firefox Process?

Thank You very much

[snkiz]

press alt-f2 then type killall firefox-bin if that doesn't work open a terminal and sudo same command

[Jayhawker]

press alt-f2 then type killall firefox-bin if that doesn't work open a terminal and sudo same command

Thank You very much. Very helpful, Really!