It seems that is related to jwplayer. Could you try updating it?

Could you check how many YouTube video formats your Firefox supports? Usually on the following page you would have the first five blue and the last red:

https://www.youtube.com/html5

Andrew said

It seems that is related to jwplayer. Could you try updating it?

Thanks for ur reply Andrew. What's JWPlayer? & where can I find it (on my pc) to update it?

jscher2000 said

Could you check how many YouTube video formats your Firefox supports? Usually on the following page you would have the first five blue and the last red: https://www.youtube.com/html5

Thanks Jscher2000 for ur help. My browser is FireFox. It supports: 1- HTMLVideoElement 2- H.264 3- WebM VP8 4- Media Source Extensions 5- MSE & H.264 It doesn't support: MSE & WebM VP9 & it says with a blue correct sign: The HTML5 player is currently used when possible.

Thanks A_M_, your HTML5 player test looks normal.

JWPlayer is a script component that sites send as part of the page. I don't think you can pre-install a particular version.

Here are some general suggestions:

When you have a problem with one particular site, a good "first thing to try" is clearing your Firefox cache and deleting your saved cookies for the site.

(1) Clear Firefox's Cache

See: How to clear the Firefox cache

If you have a large hard drive, this might take a few minutes. If you do not see the number going down on the page, you can reload it using Ctrl+r to check progress.

(2) Remove the site's cookies (save any pending work first). While viewing a page on the site, try either:

• right-click (on Mac Ctrl+click) a blank area of the page and choose View Page Info > Security > "View Cookies"
• (menu bar) Tools > Page Info > Security > "View Cookies"
• click the padlock or "i" icon in the address bar, then the ">" button, then More Information, and finally the "View Cookies" button

In the dialog that opens, the current site should be pre-filled in the search box at the top of the dialog so you can remove that site's cookies individually.

Then try reloading the page. Does that help?

If you are using a Private Browsing window, some content might be blocked by the Tracking Protection feature. This article has more information about how to spot and use the "shield" icon at the left end of the address bar: What happened to Tracking Protection?.

If problems persist, could you test in Firefox's Safe Mode? In Safe Mode, Firefox temporarily deactivates extensions, hardware acceleration, and some other advanced features to help you assess whether these are causing the problem.

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? (More info: Diagnose Firefox issues using Troubleshoot Mode)

Thanks jscher2000. I'll try these solutions