Moving mouse over the items in GM's "Website" menu is causing TypeErrors

[hurda]

Sat Jul 13 2013 18:01:17
Error: TypeError: el is undefined
Source file: chrome://greasemonkey/content/browser.js
Line: 339
 ----------
Sat Jul 13 2013 18:01:17
Error: [Exception... "'TypeError: el is null' when calling method: [nsIObserver::observe]"  nsresult: "0x8057001c (NS_ERROR_XPC_JS_THREW_JS_OBJECT)"  location: "native frame :: <unknown filename> :: <TOP_LEVEL> :: line 0"  data: no]

Windows 7, Firefox 22, new profile. First GM-version to show this error is 1.8beta2.

EDIT:
To be precise:

When the cursor hovers over "Website", in the moment the submenu is being shown, the normal TypeError is shown.
When the menu as a whole is canceled or the cursor-focus is switching elsewhere, the submenu is retracted and the Exception is shown.

[hurda]

EDIT2:
The first pair of errors of this is actually the TypeError with "Line: 339" followed by this one:

Timestamp: 13.07.2013 18:43:10
Error: [Exception... "'Error: Could not import util emptyEl:
TypeError: el is null' when calling method: [nsIObserver::observe]"  nsresult: "0x8057001c (NS_ERROR_XPC_JS_THREW_JS_OBJECT)"  location: "native frame :: <unknown filename> :: <TOP_LEVEL> :: line 0"  data: no]

After this one, triggering the same bug is followed by the TypeError and the Exception above.

[Ventero]

Ventero@8073f86 includes a possible fix for this issue. Instead of preventing event propagation from each of the submenus (which was missing for the website menu, thus causing this issue), GM_{show,hide}Popup now make sure they're only triggered for the actual monkey menu itself.