'''about:config''' > '''dom.ipc.plugins.flash.disable-protected-mode''' change it from '''false''' to '''true''' or from '''true''' to '''false'''.

I've just tried but nothing has changed, same thing

Try disabling graphics hardware acceleration in Firefox. Since this feature was added to Firefox it has gradually improved but there are still a few glitches. You will need to restart Firefox for this to take effect so save all work first (e.g., mail you are composing, online documents you're editing, etc.,) and then perform these steps: '''In Firefox 54 and below:''' # Click the menu button [[Image:New Fx Menu]] and select ''Options'' (Windows) or ''Preferences'' (Mac, Linux). # Select the ''Advanced'' panel and the ''General'' tab. # Uncheck '''Use hardware acceleration when available'''. # Close Firefox completely and then restart Firefox to see if the problem persists. '''In Firefox 55 and above''': # Click the menu button [[Image:New Fx Menu]] and select ''Options'' (Windows) or ''Preferences'' (Mac, Linux). # Select the ''General'' panel. # Under '''Performance''', uncheck ''Use recommended performance settings''. Additional settings will be displayed. #;[[Image:Fx55Performance-disableHWA|width=500]] # Uncheck '''Use hardware acceleration when available'''. # Close Firefox completely and then restart Firefox to see if the problem persists. Did this fix your problems? Please report back to us! If the problem is resolved, you should check for updates for your graphics driver by following the steps mentioned in these Knowledge base articles: * [[Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems#w_turn-off-hardware-acceleration]] * [[Upgrade your graphics drivers to use hardware acceleration and WebGL]]

i have tired again but not works again

see this answer: * https://support.mozilla.org/en-US/questions/1200404#answer-1066361

okk by starting on safe mode works all, i find a plugin that create this problem, thanks so much!

glad to help.