Boot the computer in Windows Safe mode with network support to see if that has effect.

• http://www.bleepingcomputer.com/tutorials/how-to-start-windows-in-safe-mode/
• http://www.7tutorials.com/4-ways-boot-safe-mode-windows-10

McCoy said

Not giving up just yet .... This may be a rethorical question, but in Options =>
Privacy & Security => under "Permissions": Have you checked the box "Prevent accessibility services from accessing your browser" ?

No, nothing of the sort.

cor-el said

Boot the computer in Windows Safe mode with network support to see if that has effect.

• http://www.bleepingcomputer.com/tutorials/how-to-start-windows-in-safe-mode/
• http://www.7tutorials.com/4-ways-boot-safe-mode-windows-10

Still the same issue. Also, the problem presists since the update. Both SHIFT keys cause the debugger to appear, but not on Chrome or anywhere else.

McCoy said

Another thing just came to mind : As the web console comes up when you press Shift plus the minus key : maybe you could provide a screenshot, so others can see if maybe the web console sheds some light on this .....

Here in the screenshot I'm pressing the percent and underscore hash keys, but the debugger is on for some reason. This must be a glitch on Firefox's end, because the keys to open to debugger is Control + Shift + K NOT EITHER/OR Shift + 5 OR Shift + underscore

What I'm about to ask will probably not make any sense, but would you, just as a test, disable Firefox accessibility service :

Options => Privacy & Security => under "Permissions" uncheck the box that says "Prevent accessibility services from accessing your browser" (you will then be asked to restart Firefox).

It probably won't change anything (and then you can of course check the box again), but I thought it might be worth a try ..... (everything else has failed so far).

Your screenshot shows the Performance tab selected. This specific tool has the Shift+F5 keyboard shortcut.

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

See "Creating a profile":

• https://support.mozilla.org/en-US/kb/profile-manager-create-and-remove-firefox-profiles
• http://kb.mozillazine.org/Standard_diagnostic_-_Firefox#Profile_issues

If the new profile works then 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