Quality without focus not work properly.

[taigame2366]

The option under Player > Quality without focus only work a few times after I toggle the extension or clear browser cache, some times they dont even I've done the step above.
What I did is:
Set quality option is: 1440p
Set quality without focus is: 144p
Run youtube video in firefox browser
Change mouse focus to other window like a second firefox window or another application.
The quality in not focusing youtube window reduce to 144p in frist few times.
After that, the quality keep 1440p even if I focus mouse to another window or use ALT + Tab

Did I missed anything or I should turn some config in Firefox on/off?

Please help.

update:
The extension work fine in private mode.
I've tried disable other extensions in normal mode but still not worked.
So maybe it about cache and cookies. I'm not sure about that.