What security Software are you running please ? ?

Please give your self a scan as sometimes if have something it disables browsers from working properly : https://www.malwarebytes.com/

No information was provided during making of the question which would have let us see your Extensions :

Try Firefox Safe Mode to TEST & see if the problem goes away. Firefox Safe Mode is a troubleshooting mode that temporarily turns off hardware acceleration, resets some settings, and disables add-ons (extensions and themes).

If Firefox is open, you can restart in Firefox Safe Mode from the Help menu:

• Click the menu button , click Help and select Restart with Add-ons Disabled.

If Firefox is not running, you can start Firefox in Safe Mode as follows:

• On Windows: Hold the Shift key when you open the Firefox desktop or Start menu shortcut.
• On Mac: Hold the option key while starting Firefox.
• On Linux: Quit Firefox, go to your Terminal and run firefox -safe-mode
  (you may need to specify the Firefox installation path e.g. /usr/lib/firefox)

When the Firefox Safe Mode window appears, select "Start in Safe Mode".

If the issue is not present in Firefox Safe Mode, your problem is probably caused by an extension, theme, or hardware acceleration. Please follow the steps in the Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems article to find the cause.

To exit Firefox Safe Mode, just close Firefox and wait a few seconds before opening Firefox for normal use again.

When you figure out what's causing your issues, please let us know. It might help others with the same problem.

If the above does not work : You were close to what we suggest except for the Full Version Installer.

Please : uninstall Firefox. Then Delete the Mozilla Firefox Folders in C:\Program Files , C:\Program Files(x86) & C:\ProgramData Then restart system. Then run Windows Disk Cleanup. (Note: This should be Pinned and run Weekly, If never done below expect 10's of gig's) Then run it again and click the button that says Cleanup System Files. Note: your Firefox Profile is saved. But you should make a back up before you do :

• https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles
• https://support.mozilla.org/en-US/kb/export-firefox-bookmarks-to-backup-or-transfer

Reinstall with Current Release Firefox 61.0.1 with a Full Version Installer

• https://www.mozilla.org/firefox/all/

Please let us know if this solved your issue or if need further assistance.

Hi,

Thanks for te reponse, I should have said I already scanned with Malwarebytes, all clear. Nothing reported from Windows 10 security scan either.

I already said in my question I had tried: Safe mode No add ons or extensions Uninstalling/re-installing Deleting installation folders (eventually including profile, everything I could find for as clean an install as possible.)

I do run disc cleanup regulary

Still the same, it will run in safe mode only.

Ok, the nuance of this all is to get information any way you can.

So it works in Safe Mode as you said : ok then please follow the instructions on the information given regarding running in Safe Mode.

There is lots more to it like now follow trouble shooting your Extensions as per the link in the 1st post.

You did not answer what Security Software you are running ?

Pkshadow said

Ok, the nuance of this all is to get information any way you can. So it works in Safe Mode as you said : ok then please follow the instructions on the information given regarding running in Safe Mode. There is lots more to it like now follow trouble shooting your Extensions as per the link in the 1st post. You did not answer what Security Software you are running ?

There are no add ons or extensions installed, completely fresh install. The only security software I have is W10 Windows Defender Security Centre plus Malwarebytes.

Hi, so weird. You did the install with the Full Version Installer ? As that is important part of doing the clean install and can make or break it if ignore it.

I know your running the same Edge version as I am so you must be on version 1803 of Win10.

Please follow this for WIn10 Registry & System File fix, Note will download new files if needs them.

1)Use the Windows key + X keyboard shortcut to open the Power User menu and select Command Prompt (Admin). 2) Type or Copy/Paste the following command and press Enter: 3) DISM /Online /Cleanup-Image /RestoreHealth Reboot after.

Reinstall with Full Version Installer : https://www.mozilla.org/firefox/all/

After this might have to wait for a Full Version installer on the next release. Is so weird since deleted the Profile and the folders. Some one else may have a idea.

Please : To be Checked and turned off unless needed for accessibility : Please : go to the Firefox 3 Bar Menu --> Options --> Privacy & Security panel and under Permissions check (put a tick in the box) the setting to Prevent Accessibility Services from accessing your browser.

A option to check : Firefox Extended Release Version : Firefox ESR does not come with the latest features but it has the latest security and stability fixes.

• https://support.mozilla.org/en-US/kb/switch-to-firefox-extended-support-release-esr

If do please :

• https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles
• https://support.mozilla.org/en-US/kb/export-firefox-bookmarks-to-backup-or-transfer

Well, fixed it. Under Nvidia control panel, in 3d settings Firefox was set to high performance NVIDIA processor. Set this to integrated graphics and all good.

Strange thing is, I never changed this setting before and everything was working until very recently.