Try the Firefox version from the official Mozilla server if you currently use a version from the repositories of your Linux distribution.

• https://www.mozilla.org/en-US/firefox/all/

Start Firefox in Safe Mode to check if one of the extensions ("3-bar" menu button or Tools -> Add-ons -> Extensions) or if hardware acceleration is causing the problem.

• switch to the DEFAULT theme: "3-bar" menu button or Tools -> Add-ons -> Appearance
• do NOT click the "Refresh Firefox" button on the Safe Mode start window

• https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-using-safe-mode
• https://support.mozilla.org/en-US/kb/troubleshoot-extensions-themes-to-fix-problems

I already did try safe mode. I will try installing the official version to see if that makes a difference. The 3-bar menu is the thing that's not working, so is there a way to switch to the default theme without it working?

I am now running the version from the link you included in safe mode with the default theme. The 3 menu bars and the library button still do not open any kind of menu.

Any error messages when you start Firefox via a terminal window?

No, nothing.

Update: I've also found that the information/secure connection/desktop notification box no longer does anything when clicked as well. It seems to be all the buttons on that row no longer respond to left clicks. Right clicking still gives me what I believe are the normal options. (Menu bar, bookmarks toolbar, customize)

Hello, it may be a graphical issue. Is your distribution up to date?

I just updated everything. Unfortunately, the problem persists.

Any ideas which packages could cause this problem? I can try downgrading them to an older version to see if that might restore it.

(I suspect the graphics driver is the problem... the buttons appear to work, they are just invisible. just which program actually is causing this is the question)

Another thing you could try is using another GTK3 theme on the OS as Firefox does not use KDE themes.

I tried that now. Still no luck. It worked fine until recently and I haven't touched that. I did update my graphics fairly recently so it's possible that was the issue. However, I believe this problem did not show up until a day or two ago, whereas I upgraded them like a week ago.

I managed to fix the problem. It was a problem with my graphics drivers and not with firefox. Thank you for the help.