"this.docShell is null" error while opening HttpFox in Firefox 11

[GoogleCodeExporter]

What steps will reproduce the problem?
1. Start Firefox.
2. Open HttpFox (in menu: View / HttpFox).
3. In error console a series of "this.docShell is null" errors (3 of them) 
appear and the "Start" button in HttpFox does nothing (it does not start 
capture of HTTP requests).

What is the expected output? What do you see instead?

The expected "output" is that HttpFox starts capturing requests when the 
"Start" button is pressed.

What version of the product are you using? On what operating system?

Firefox 11 and HttpFox 0.8.10 on both Ubuntu (10.10) and Mac OS X (10.6.8) and 
Windows (XP).

Please provide any additional information below.

HttpFox worked in Firefox 10.0.2 and failed to work after the upgrade to 
Firefox 11. Downgrading to Firefox 10.0.2 makes it work again.

Original issue reported on code.google.com by zsolt.mu...@gmail.com on 20 Mar 2012 at 8:54

[GoogleCodeExporter]

Sorry for my incompetence: it turned out that another extension (F.B. Purity 
v6.6.2) caused a number of problems (not just with HttpFox) in Firefox 11. :-(
Please, close this issue since HttpFox is not to blame for it.

Original comment by zsolt.mu...@gmail.com on 22 Mar 2012 at 1:26