Those are likely games that use the Shockwave Flash plugin. You can try to disable multi-process tabs in Firefox to see if that has effect. You can disable multi-process tabs in Firefox by setting the related prefs to false on the about:config page. *browser.tabs.remote.autostart = false *browser.tabs.remote.autostart.2 = false *http://www.ghacks.net/2016/07/22/multi-process-firefox/ You can open the <b>about:config</b> page via the location/address bar. You can accept the warning and click "I'll be careful" to continue. *http://kb.mozillazine.org/about:config

Thank you so much for your reply. I'm afraid though this didn't have any effect.

Clear the cache and remove the cookies from websites that cause problems via the "3-bar" Firefox menu button (Options/Preferences). "Clear the cache": *Firefox/Options/Preferences -> Advanced -> Network -> Cached Web Content: "Clear Now" "Remove the cookies" from websites that cause problems. *Firefox/Options/Preferences -> Privacy -> "Use custom settings for history" -> Cookies: "Show Cookies" Start Firefox in <u>[[Safe Mode|Safe Mode]]</u> to check if one of the extensions ("3-bar" menu button or Tools -> Add-ons -> Extensions) or if hardware acceleration is causing the problem. *Switch to the DEFAULT theme: "3-bar" menu button or Tools -> Add-ons -> Appearance *Do NOT click the "Refresh Firefox" button on the Safe Mode start window *https://support.mozilla.org/kb/Safe+Mode *https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes ---- You can check for problems with current Shockwave Flash plugin versions and hardware acceleration in Firefox and try this: *make sure you have the latest Flash version:<br>*https://get.adobe.com/flashplayer/otherversions/ *check for updates for your graphics drive drivers<br>https://support.mozilla.org/kb/upgrade-graphics-drivers-use-hardware-acceleration *disable protected mode in the Flash plugin (Windows Vista and later)<br>https://support.mozilla.org/kb/adobe-flash-protected-mode-firefox *disable hardware acceleration in the Flash plugin<br>https://helpx.adobe.com/flash-player/kb/video-playback-issues.html *disable hardware acceleration in Firefox<br />https://support.mozilla.org/kb/upgrade-graphics-drivers-use-hardware-acceleration See also: *https://support.mozilla.org/kb/keep-flash-up-to-date-and-troubleshoot-problems *http://kb.mozillazine.org/Flash#Troubleshooting