You will need to install a user script manager extension to install this script.
On Firefox, if you has set
dom.enable_performance_observer = false a few sites may break. For instance, hash links don't work in GitHub. Example (click any index link in the center of the page, like "For version 2.0 and later").
This tiny script fakes
PerformanceObserver to unblock these pages. Currently restricted to pages I know are broken. You can set user-includes/matches to enable this script in other pages.
Tested with FireMonkey, but should work with any UserScripts Manager.