If the issue occurred after an update, it's possible that the update did not install correctly and damaged your Firefox installation.

To fix this, you can safely download Firefox again from the Mozilla website and install it over top of your current installation. This will repair any damaged files in the installation and will hopefully fix the issue that you are having.

You should be able to do this installation without a risk of losing the data stored in your Firefox profile (bookmarks, settings, etc). However, if you are concerned about losing this data, you can do a manual backup before completing the installation. See the Back up and restore information in Firefox profiles documentation for more information.

Does this fix the issue? Let us know.

I do have the same issue, makes the browser completely unusable.

Reinstalling Firefox did not solve my issue.

This is what the screen looks like, including the white section on top. Clicking it does nothing (can't drag drop the window with it), it clicks through and acts like you clicked the window behind it.

Maybe worth noting, I had enabled the option that shows the menu bar on top.

Anyone know how to solve this? I'm using Chrome for now, but that's not really a solution that I enjoy.