This issue can be caused by an extension that isn't working properly.

Did any extension updated around that time?

Start Firefox in Safe Mode to check if one of the extensions (Firefox/Firefox/Tools > Add-ons > Extensions) or if hardware acceleration is causing the problem (switch to the DEFAULT theme: Firefox/Firefox/Tools > Add-ons > Appearance).

• Do NOT click the Reset button on the Safe Mode start window.

• If you have many extensions then first enable half of the extensions to test which half has the problem.
• Continue to divide the bad half that still has the issue until you find which one is causing it.

• https://support.mozilla.org/kb/Safe+Mode
• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes

Thank you for your reply

Well, firefox was updated so i guess many of add-ons were also updated when i restarted (i restarted after a few days) i was thinking maybe this is a change in new firefox!

i don't have the problem in Safe Mode but its gonna take some time finding that "one" add-on as i have almost 40

Thanks again

You're welcome

Note that you can check on the about:addons page for recent updates (Click the Tools, gear shaped button).