Open Firefox. Right-click on the Firefox icon and select Open New Window. If a new window opens, close the first window using its icon.

FredMcD said

Open Firefox. Right-click on the Firefox icon and select Open New Window. If a new window opens, close the first window using its icon.

The browser does not open. As I wrote firefox is in the task manager running at 14% CPU but the is no screen output at all - almost as though I had not started firefox. I started ff nornally and as administration. My ID is as an administrator.

So, you are saying there is no Firefox icon on the computer's taskbar?

Let’s do a full clean re-install;

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)

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 ++++++++++++++++++++++++++++ Look for, and remove any Mozilla or Firefox program folders. Do not remove the Mozilla Thunderbird folder if there is one.

Do Not remove the profiles folder.

After rebooting the computer, run a registry scanner if you have one. Then run the installer. +++++++++++++++++++++++++++ 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

21.3.2018 @fredmcd

MAny thanks for your comment.

No, the Icon was on screen - hence the ability to start Firefox. It seem to do something that occupies 14% of the CPU but then nothing appears on my screen. A strange behaviour, since two day ago it was fine and I made no changes to it. I also - two day ago - I deleted firefox over the Windows remove programmes and then reinstalled it. Still no change. Opera and Edge both function well. I accept the problem is specific to my computer but I have no idea what.

FredMcD said

Open Firefox. Right-click on the Firefox icon and select Open New Window. If a new window opens, close the first window using its icon.

Bonzadog said

The browser does not open.

Bonzadog said

the Icon was on screen

Follow my instructions above.

1) a click on the desktop icon to start - confirmed in task manager - nothing happens 1a) Left click get the hour glass then nothing

2) clicking right on the icon only gives the usual Open .... Properies menu. This is what I expect when I click on an Icon. There is no Open New WIndow I think the Firefox must be on screen for that.

https://support.mozilla.org/en-US/kb/changes-toolbars-and-window-sizes-are-not-saved You may have corrupt xulstore.json or Localstore.rdf file.

Close Firefox. Open your file browser to this hidden location:

• Mac: *~/Library/Application Support/Firefox/Profiles
• Linux: *~/.mozilla/firefox/Profiles
• Windows: %AppData%\Mozilla\Firefox\Profiles
• *C:\Users\<user>\AppData\Roaming\Mozilla\Firefox\Profiles
• Windows XP: C:\Documents and Settings\<user>\Application Data
  \Mozilla\Firefox\Profiles\

Search for the above files. Then rename or delete them. Restart Firefox.

Appreciate you help - but it did not work.

I bought a reno uninstaller programme and reinstalled firefox then uninstalled with the new uninstaller. Still did not work after the reboot and new install. This is indeed a rather toothsome problem.

Use these links to create a new profile. Use this new profile as is. Is the problem still there?

http://kb.mozillazine.org/Profile_folder_-_Firefox#Navigating_to_the_profile_folder

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

https://support.mozilla.org/en-US/kb/how-run-firefox-when-profile-missing-inaccessible

https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles

Type about:profiles<enter> in the address bar.

Thank you that solved the problem.

I changed the old default to default-ng because when I tried to delete I received a "not responding" message. After a firefox start all was OK.

Again thanks, and you are good for a couple of Pils should you ever be in Northern Germany....

Glad to help. Safe Surfing.