Is this a message after Firefox has crashed, or does Firefox continue working normally after you click off the message?

Does it only appear at startup, or does it appear more often? It would be helpful to better understand the circumstances.

Here's what happened today.

1. I received a popup that a new Firefox update was ready to be downloaded.

2. Firefox crashed before I was able to download the update, and I was unable to restart Firefox immediately, so I rebooted my PC.

3. After my PC rebooted, I launched Firefox and it automatically installed the update.

4. Since then, I've received the error message. It pops up every now and then -- probably once every 10-15 minutes or so. When I click "OK", Firefox continues working.

One possible issue is an add-on that isn't compatible with the new version of Firefox. You can check for extension updates on the Add-ons page. Either:

• Ctrl+Shift+a
• orange Firefox button (or Tools menu) > Add-ons

In the left column, click Extensions. Then click the "gear" button above the list and choose "Check for Updates".

If the problem continues after updating, since the problem is so regular, I think it would make sense to test in Firefox's Safe Mode for an hour. That's a standard diagnostic tool that deactivates extensions, advanced script technologies, and some custom settings. More info: Diagnose Firefox issues using Troubleshoot Mode.

You can restart Firefox in Safe Mode using

Help > Restart with Add-ons Disabled (Flash and other plugins still run)

In the dialog, click "Start in Safe Mode" (not Reset)

Any difference?

Operating in safe mode doesn't seem to make a difference. The error message seems to appear after I click on a URL in Microsoft Word or Outlook.

If I uninstall Firefox, then reinstall it, do you think that will make a difference?

Okay, that's interesting. When you click a link in an external application, a few different things happen. Windows uses the information in the registry to open the link in your default browser. In the process, a new window or new tab may be opened.

Do you get the same error if you open a shortcut to a web page on your desktop (or some other saved shortcut such as in you Windows Favorites folder)?

Do you get the same error if you paste a URL into the Start menu Find box such as http://www.mozilla.org/ and then click the URL to open it? (Example attached)

Does the error occur if you simply open a new window in Firefox using Ctrl+n?

Reinstalling Firefox should refresh the registry settings for Firefox as default browser, but a less disruptive way to do that is to make a double-switch: make IE your default browser, then make Firefox your default browser again.

• First, have Internet Explore make itself the default browser: http://windows.microsoft.com/en-us/internet-explorer/make-ie-default-browser
• Second, have Firefox make itself the default browser: Make Firefox your default browser

I downloaded several Windows updates last night and also reset Firefox and since then (before I received your two emails above), I haven't gotten the popup. I tried again this morning to opening URLs from Outlook and Word, and the popup did not appear. Apparently, my Windows was just outdated.

So sorry to have troubled you!