Start Firefox in Diagnose Firefox issues using Troubleshoot Mode to check if one of the extensions is causing the problem (switch to the DEFAULT theme: Firefox (Tools) > Add-ons > Appearance/Themes).

• Don't make any changes on the Safe mode start window.
• https://support.mozilla.com/kb/Safe+Mode

If it does work in Safe-mode then disable all extensions and then try to find which is causing it by enabling one at a time until the problem reappears.

• Use "Disable all add-ons" on the Safe mode start window to disable all extensions.
• Close and restart Firefox after each change via "File > Exit" (Mac: "Firefox > Quit"; Linux: "File > Quit")

In Firefox 4 you can use one of these to start in Safe mode:

• Help > Restart with Add-ons Disabled
• Hold down the Shift key while double clicking the Firefox desktop shortcut (Windows)

• https://support.mozilla.com/kb/Troubleshooting+extensions+and+themes

HI, Thanks for that. I have been here already. All is fine in safe mode, but with all add-ons disabled, I stll get the message. Hope someone can help.

Are you using the default theme ?

Did you check that some extensions added by external programs didn't get enabled?

Can you post a list of the extensions?

See Use the Troubleshooting Information page to help fix Firefox issues

No Extensions, No appearances. Snips of screen attached. Plug-ins are now re-enabled, but it made no difference when they were all disabled. What else is there? Thanks Steve

Do a clean (re-)install:

• Download a fresh Firefox copy and save the file to the desktop.
• Firefox 4.0.x: http://www.mozilla.com/en-US/firefox/all.html

• Uninstall your current Firefox version and remove the Firefox program folder before installing that copy of the Firefox installer.
• Do not remove personal data if you uninstall the current version.
• It is important to delete the Firefox program folder to remove all the files and make sure that there are no problems with files that were leftover after uninstalling.

Your bookmarks and other profile data are stored elsewhere in the Firefox Profile Folder and won't be affected by a reinstall, but make sure that you do not select to remove personal data if you uninstall Firefox.

OK, I'll do that. I will let you know how I get on Wish me luck Regards

Now I am OK but baffled. I did all that as above, but it was exactly the same. I then did it again, but turned the computer off and restarted it after deleting the Firefox folder...Still the same. Then, not sure why, I started Firefox from the shortcut but with "Run as administrator" and it started fine and with no pop-up. ..and no pop-up since. Hopefully now OK, and I will not be back here to report a relapse. Thanks to anyone and everyone who contributed. I hope this helps someone else as well.

In FireFox disabling the Crawler Toolbar gets rid of it for me

You are kidding. Right? You'll let me know? I have updated to 4 three times and had this problem and reverted back to older version. You still haven't solved the problem? May be changing browser soon.

Hi Louray. I don't quite follow your last comment, but it has worked for me. Since that one time running as administrator the problem has just gone away. No popups.. nothing. Hope that helps

I was so thrilled to see this post! I've been researching this problem for a couple of months, and every time I researched it, I could only find information about disabling add ons. I have the exact same problem. I disabled all the add ons and still kept getting the error.

I'm going to try to follow your suggestions, Steve. I'm not sure how to "run as administrator," but I'm going to give it a shot. I have been on a summer break from my job for the last couple of months, but in a few weeks I'll be back to work, and I can't continue to deal with this annoying pop up. If I don't get a solution, I'll have to revert back to Firefox 3.6, which was working just fine before I upgraded.

Thanks for posting!

I started up in safe mode and then found that the DataVault (program I had for explorer from Ascendo) addon was the culprit.