I am not familiar with your platform or build, but as general questions:

(1) Do other internal pages work? For example: Help > More Troubleshooting Information

(2) Assuming you can open a new tab (Ctrl+T), if you type or paste about:preferences and press Enter/Return (or click the arrow), will Firefox display the Settings page?

(3) Are there any active policies listed on the about:policies page? (That could have clues about modifications in your build.)

How did you install Firefox?

Does it still happen with the flatpak package?

I am not familiar with your platform or build, but as general questions: (1) Do other internal pages work? For example: Help > More Troubleshooting Information (2) Assuming you can open a new tab (Ctrl+T), if you type or paste about:preferences and press Enter/Return (or click the arrow), will Firefox display the Settings page? (3) Are there any active policies listed on the about:policies page? (That could have clues about modifications in your build.)

1) No, this does not work either. 2) Yes, this works. 3) I get to see the following: Active The Enterprise Policies service is inactive.

So I think not.

It appears that every Dropdown menu in Firefox doesn't work. (Like changing the language on this site at the bottom) I can open it, but when I press an item in it, nothing happens.

How did you install Firefox? Does it still happen with the flatpak package?

I installed Firefox according to: https://support.mozilla.org/en-US/kb/install-firefox-linux Then I followed: Install Firefox .deb package for Debian-based distributions

Because you mentioned flatpak, I installed flatpak according to the instructions for Ubuntu. Then I tried and went to install firefox, I just got an error: Error: Flatpak system operation Deploy not allowed for user error: Failed to install org.freedesktop.Platform: Flatpak system operation Deploy not allowed for user

Both problems are probably caused because I might miss a package. I mean WSL gives you a bare bones minimal install. (Even Arch is not this bare bones)