I searched around about this and didn't see any obvious solution.

Could you test in Firefox's Safe Mode? That's a standard diagnostic tool to deactivate extensions, hardware acceleration, and some advanced features of Firefox. More info: Diagnose Firefox issues using Troubleshoot 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 difference?

Thanks. It worked in safe mode. but i am not sure which add-on is doing this. works fine on opera

Do any of your extensions interact with media players, for example, downloaders/recorders, or do any of your extensions possibly block cookies?

Have download helper and 2 ad blocks. all for a long time with no problem. guess i can disable one at a time to test.

those 3 made no difference, still not work with them disabled. guess opera will be my browser. update avg regularly.

turned avg off. still not work

Fixed, either https everywhere or nimbus screen capture. Thanks

was https add-on

Thanks for reporting back. HTTPS Everywhere is a great idea, but on many sites that are not designed for HTTPS, it causes these mysterious problems.