Do you notice any pattern as to which sites cause the lockup(s)? Could you try starting up in Firefox's Safe Mode? That's a standard diagnostic tool to deactivate extensions and some advanced features of Firefox. More info: [[Troubleshoot Firefox issues using Safe Mode]]. ''If Firefox is not running:'' Hold down the Shift key when starting Firefox. ''If Firefox is running:'' You can restart Firefox in Safe Mode using either: * "3-bar" menu button > "?" button > Restart with Add-ons Disabled * Help menu > Restart with Add-ons Disabled and OK the restart. ''Both scenarios:'' A small dialog should appear. Click "Start in Safe Mode" (''not'' Refresh). Any improvement? ---- One possible culprit that isn't disabled in Firefox's Safe Mode is the protected mode feature of the Flash player plugin. That feature has security benefits, but seems to have serious compatibility issues on some systems. You can disable it using the Add-ons page. Either: * Ctrl+Shift+a * "3-bar" menu button (or Tools menu) > Add-ons In the left column, click Plugins. On the right side, find "Shockwave Flash" and click the More link. Then ''uncheck'' the box for "Enable Adobe Flash protected mode" and try that for a day to see whether it helps.