Start Firefox in Safe Mode {web link}

A small dialog should appear. Click Start In Safe Mode (not Refresh). Is the problem still there?

When I start the browser in safe mode, the exact same thing happens.

Let’s do a full clean re-install;

Note: Firefox comes in three or more folders on all computers. They are;

Maintenance: (Programs Folder) <Windows Only> Firefox itself: (Programs Folder) And two folders in the profile of each user on the computer for each Firefox profile for that user.

If you remove the Firefox folder, the user profiles would not be affected.
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Download Firefox For All languages And Systems {web link}

Save the file. Then Close Firefox.

Using your file browser, open the Programs Folder on your computer.

Windows: C:\Program Files C:\Program Files (x86) Note: Check Both Folders

Mac: Open the "Applications" folder. https://support.mozilla.org/en-US/kb/how-download-and-install-firefox-mac

Linux: Check your user manual. If you installed Firefox with the distro-based package manager, you should use the same way to uninstall it. See Install Firefox on Linux; https://support.mozilla.org/en-US/kb/install-firefox-linux

If you downloaded and installed the binary package from the Firefox download page, simply remove the folder Firefox in your home directory. http://www.mozilla.org/firefox#desktop
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Look for, and remove any Mozilla or Firefox program folders. Do not remove the Mozilla Thunderbird folder if there is one.

Do Not remove any profile folders.

After rebooting the computer, run a registry scanner if you have one. Then run the installer.
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If there is a problem, start your Computer in safe mode and try again.

http://encyclopedia2.thefreedictionary.com/Linux+Safe+Mode This shows how to Start all Computers in Safe Mode; Free Online Encyclopedia

Unfortunately, this didn't work either. It sure looked like it would work for a bit there, but it only lasted for about 25 seconds before Firefox force closed again. And, once again, no Crash Helper popup.

Are you getting a crash dialog from Windows, or nothing at all? The Windows Event Viewer, Applications log might have more information about the crashes if Windows is killing Firefox (i.e., Firefox isn't exiting for some reason). This sometimes helps identify conflicting applications or drivers.

No crash dialog, nothing at all. It's as if someone had closed the browser via the UI.

I'll check the Windows Event Viewer tomorrow to see if there's anything there. Since it's an observable phenomenon, it should be pretty easy to know if there's anything there.

All right - turns out the Windows Event Viewer tells us something:

Faulting application name: firefox.exe, version: 76.0.1.7432, time stamp: 0x5eb403e6 Faulting module name: PayloadRestrictions.dll, version: 10.0.17763.1, time stamp: 0x7885c70a Exception code: 0xc0000409 Fault offset: 0x000000000003b614 Faulting process id: 0x1bf8 Faulting application start time: 0x01d62da298efe57c Faulting application path: C:\Program Files\Mozilla Firefox\firefox.exe Faulting module path: C:\WINDOWS\SYSTEM32\PayloadRestrictions.dll Report Id: 5ce6761f-90af-4006-a3aa-66f6b47c290d Faulting package full name: Faulting package-relative application ID:

A quick search for exception code gives me several issues in the mozilla bug tracker, e.g. https://bugzilla.mozilla.org/show_bug.cgi?id=1509748

But since this has been around for a good long while now, I'm not that optimistic about seeing it fixed anytime soon :(

Perhaps not coincidentally, another user posted a thread about EAF today. Could I suggest you confer/commiserate and see whether you can find a workaround: https://support.mozilla.org/questions/1287245

So done, but I don't see any of the known workarounds working. Looks like I'll have to stick with an old version of Firefox or use a different browser until this gets fixed in a future Windows update (whenever that gets rolled out to my machine).