Could be a problem with the modifications that Ubuntu makes to Firefox.

Start Firefox in Safe Mode to check if one of the extensions (Firefox/Tools > Add-ons > Extensions) or if hardware acceleration is causing the problem.

• Switch to the DEFAULT theme: Firefox/Tools > Add-ons > Appearance
• Do NOT click the Reset button on the Safe Mode start window

• https://support.mozilla.org/kb/Safe+Mode
• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes

Try the version from the official Mozilla server if you currently use a version from the repositories of your Linux distribution.

Hi thanks for your help. I have tried safe mode and it is still happening. I tried uninstalling and reinstalling firefox also.

I have discovered one thing, however, which has left me even more perplexed. This same problem exists in Firefox in both Windows and Ubuntu. I have no idea what is causing the problem! Can you advise me on this?

You aren't using the same profile in a dual boot configuration (Windows, Linux)?

Create a new profile as a test to check if your current profile is causing the problem.

See "Creating a profile":

• https://support.mozilla.org/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.

• http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox

By profile I'm assuming you mean user accounts?

Lubuntu has 3 different accounts plus a guest account as it is a family computer. The problem appears on every account.