The XULRunner 1.9.1 has nothing to do with the Firefox XULRunner runtime despite the name.

The XULRunner 1.9.1 extension is considered malware and you should remove it.

• /questions/743526
• /questions/749007

Neither of the above links helped to resolve my issue. No anti-spyware\malware programs found anything related to this issue.

I was finally able to resolve this problem by following these steps:

Required Tool:

• Bulleted list item Agent Ransack (fast file finder for windows) http://agentransack.com

With FF4 Add-ons Manager opened and Extensions tab selected, I right-clicked on XULRunner and selected "Show More Information" and found that the last update of this program was 07/30/2010.

Using Agent Ransack, I search my hard drive for all files modified after 07/29/2010 and before 07/31/2010 containing the text "1.9.1". On my system, this pointed to c:\Users\[MyUserName]\AppData\Local\{39970BED-10E8-4B50-9E99-DE239C3974BD}\install.rdf. This folder is actually defined as a Chrome components (go figure). Your search result will certainly point to another GUID folder, but the results should be the same.

With FF4 closed, I deleted the folder c:\Users\[MyUserName]\AppData\Local\{39970BED-10E8-4B50-9E99-DE239C3974BD}, then restarted FF4 and XULRunner 1.9.1 was no longer in the Extensions list.

I found an "easier" way to do this.

As I had Add-on Compatibility Reporter 1.1 installed I just reported the add-on as not working. I then looked at the report generated (right click on XULRunner add-on and select Show Compatibility Reports).

This gave me a report link with the folder / directory name of the add-on as the title. {F3F0B3BA-D86A-4478-961D-3B24C2D0EAF1} Compatibility Reports

https://addons.mozilla.org/en-US/firefox/compatibility/reporter/%7BF3F0B3BA-D86A-4478-961D-3B24C2D0EAF1%7D?works_properly=0

I was then able to locate this folder (with FireFox closed) and rename it.

C:\Documents and Settings\Tony.TONY-SR1619\Local Settings\Application Data\{F3F0B3BA-D86A-4478-961D-3B24C2D0EAF1}

C:\Documents and Settings\Tony.TONY-SR1619\Local Settings\Application Data\WCS{F3F0B3BA-D86A-4478-961D-3B24C2D0EAF1}

When I open up FireFox again the blasted XULRunner add-on was no longer there.

I then scanned this folder ,again, with MalwareBytes - no malware? So I zipped the folder up and sent it to VIRUSTOTAL - 4 hits. My ViirusTotal scan

For more details of what I did have a look here. WCS.DOODLEKIT.COM