Not sure how this follows with Windows O/S but when you uninstalled FF did you delete the Mozilla folder before reinstalling FF?

You can check the Web Console (Tools -> Web Developer) for messages about blocked content and about the presence of mixed or unsafe content.

• https://developer.mozilla.org/en/Tools/Web_Console

You can check the Network Monitor to see if content is blocked or otherwise fails to load.

• https://developer.mozilla.org/en/Tools/Network_Monitor

If necessary use "Ctrl+F5" or "Ctrl+Shift+R" (Mac: Command+Shift+R) to reload the page and bypass the cache to generate a fresh log.

If you use extensions ("3-bar" menu button or Tools -> Add-ons -> Extensions) that can block (wanted) content (Adblock Plus, NoScript, Disconnect, Ghostery, Privacy Badger, uBlock Origin) always make sure such extensions do not block (wanted) content.

• make sure your extensions and filters are updated to the latest version
• https://support.mozilla.org/en-US/kb/troubleshoot-extensions-themes-to-fix-problems

Firefox shows the shield icon at the left end of the location/address bar in case content is blocked by Tracking Protection.

• click the shield icon for more detail and possibly disable the protection
• You can check the Web Console by Tracking Protection
• "3-bar" menu button or Tools -> Web Developer
• https://support.mozilla.org/en-US/kb/tracking-protection-firefox

Hello oxfried,

Do you by any chance have this extensions installed  :

https://addons.mozilla.org/en-US/firefox/addon/youtube-adblock-adblocker/?src=rating  ?

If so, would you please disable it - that solved the problem for others, who had YouTube Adblock installed .......

Thank you for all your helps guys ! cor-el solution solved my problem. I have too much privacy addons installed ! I have removed few of them and YouTube come back again

Thank you Guys !