Thanks for the report. 1-star review for UltimaDark is quite harsh given the significant amount of work that has gone into this project !
This behavior is not reproducible on my side, and YouTube works normally for other users, including with UltimaDark enabled. Excluding YouTube or disabling the extension should prevent any impact, so this points to a setup-specific issue, most likely a conflict with another browser extension or a particular browser configuration.
----> https://github.com/ThomazPom/Moz-Ext-UltimaDark/issues
To investigate this properly, please open an issue and include:
Browser name and version
Other installed extensions
Any relevant console errors
I’ll take a look and see what’s going on. Without those details, I don’t have enough information to diagnose the problem.
Removing the extension is of course a valid workaround for now, but if you want this fixed, an issue report is the right place to continue.