There is a known issue in Firefox 70 that prevents some pages or page elements using dynamic Javascript (like YouTube or Facebook) from loading properly.
A Firefox 70.0.1 update was released that should resolve the problem. Please update Firefox to the latest release.
If you are unable to update Firefox, here is a temporary workaround:
- Type about:config in the address bar and press EnterReturn.
A warning page may appear. Click to go to the about:config page. - Search for dom.storage.next_gen
- Double-click on the dom.storage.next_gen preference to toggle its value to false.