Try disabling any third-party antivirus or security software.

Does it still happen when rebooting in Windows Safe Mode?

I am using Bitdefender. I turned off everything I could find but still the same.

Just to be safe, I downloaded Malwarebites and the Kaspersky Root scanner and let them both run. They both didn't find anything.

When starting in Windows Safemode (Nr. 5 with Network support) my Wifi-card is being disabled. Firefox starts normal but can't of course connect to any pages.

Reinstall the Visual C++ Redistributable.

Go to about:third-party in the address bar and try disabling third-party modules.

Check your file system integrity by running sfc /scannow from command prompt.

I re-installed the Visual C++ Redistributables - restarted the computer and it is still the same

I ran sfc /scannow - Windows found some corrupted files and was able to fix them, but this didn't solve my problem either (rebooted computer after running it).

When going to about:third-party I have three entries (see image) but no block button. Fixing the missing block button was not possible because about:config tells me that the browser.launcherProcess.enabled is set to true, but about:support tells me that the launcher process is "disabled due to failure" (but still no crash reports)

Update:

I uninstalled both Start11 and Opus Explorer, and made sure their respective dll's weren't found, but neither of them are responsible for my problem. Sigh....

Update 2:

So after having done all that, I go back to about:third-party and it shows me completely different third-party dll, even though both Start11 and Opus Explorer have been re-installed and my Nvidia-Drivers have never been uninstalled at all? (see picture)

This time it is Bitdefender.....

Update 3:

Uninstalled Bitdefender - rebooted and it is still the same Uninstalled my Nvidia-Drivers - no luck as well

I am about to give up on Firefox.

What URL in the tab is this about ?

Did you check the Browser Console to see whether any thing is reported about this tab crash ?

It's about all and any possible URL's not a specific one.

I attached the contents of the browser console. I don't know enough for me to understand any of it.

You can check for issues with Storage (indexedDB).

• https://firefox-storage-test.glitch.me/

You can create a new profile as a quick test to see if your current profile is causing the problem.

See "Creating a profile":

• https://support.mozilla.org/en-US/kb/profile-manager-create-remove-switch-firefox-profiles

If the new profile works, you can transfer files from a previously used profile to the new profile, but be cautious not to copy corrupted files to avoid carrying over problems.

• https://support.mozilla.org/en-US/kb/recovering-important-data-from-an-old-profile

Thanks for your continous support. As I said initially, I had previously erased all data pertaining to Mozilla and had done a new install. Creating a new profile using your method didn't change anything either, unfortunately.

And I can't use the storage-test-glitch link, as that tab crashes constantly as well.

As a last resort, I tried to uninstall Firefox, manually delete all Mozilla or Firefox Folders - rebooted the computer - cleaned the registry - rebooted again, and then re-installed Firefox. But it is still the same.