Hi,

Launch Firefox in Safe Mode. All extensions and themes will be disabled. Now try to open multiple windows and/or tabs. If it works, it proves you have a corrupt profile probably caused by a bad extension (or upgrade).

To make a new profile:

• Close Firefox
• Click on windows start button
• %APPDATA%\Mozilla\Firefox\Profiles\ in the Search box at the bottom of the Start menu (without hitting Enter).
• A list of profiles will appear
• Change the name of the "default" folder
• Restart Firefox

If this solved your problem, you can install your addons, or just copy them from the old default folder (which you have changed the name) to the new one.

Kind regards, Joren

Thanks, Joren, but that didn't work. Even in safe mode, the problem persists. I tried Internet Explorer, and it also had the same problem. So, I guess this is now the wrong place to ask, but I'm wondering if anyone has any ideas.

Like I said, it works just fine on other computers, so I'm guessing it's not a problem with my router.