only the curernt gmail is suffering this, i use the same URL in other account and its playing properly and it work without signing in.

Many site issues can be caused by corrupt cookies or cache.

Warning ! ! This will log you out of sites you're logged in to. You may also lose any settings for that website.

• Delete cookies to remove the information websites have stored on your computer {web link}

• How to clear the Firefox cache {web link}

If there is still a problem, Start Firefox in Safe Mode {web link} by holding down the <Shift> (Mac=Options) key, and then starting Firefox.

A small dialog should appear. Click Start In Safe Mode (not Refresh). Did this help?

While you are in safe mode;

Try disabling graphics hardware acceleration in Firefox. Since this feature was added to Firefox it has gradually improved but there are still a few glitches.

How to disable Hardware Acceleration {web link}

i did all of the above mentioning already, the only thing it works is when i sign out from YouTube and when i use another google account. the video URL just work fine in chrome. i even refresh , uninstall and install it again.

Its a very common issue which Firefox users face... The quick way to solve is to Reboot your device and clear RAM space.This works 98%.

even when i go back to youtube home the player is still playing. i think 16GB is enough RAM. The thing is all is working well if my youtube is sign off. if i sign in the problem presist.