Firebug returning constant nsLoginManager error

I'm working on a project, and Firebug keeps on reporting a nsLoginManager error (which has nothing to do with my project.

It is disconcerting to see "3 errors" in the status bar on my browser only to open it up and see it's the effing nsloginmanager error message... AGAIN.

Here is the error:

[Exception... 
"Component returned failure code: 0x80004001 (NS_ERROR_NOT_IMPLEMENTED)  
[nsIRequest.name]"  nsresult: "0x80004001 (NS_ERROR_NOT_IMPLEMENTED)"
location: "JS    frame :: file:///Applications/Firefox.app/Contents/MacOS/
components/nsLoginManager.js :: anonymous :: line 315"  data: no]file:///
Applications/Firefox.app/Contents/MacOS/components/nsLoginManager.js
Line 315

Here is the relevant code form nsLoginManager.js:

        onStateChange : function (aWebProgress, aRequest,
                              aStateFlags,  aStatus) {

        // STATE_START is too early, doc is still the old page.
        if (!(aStateFlags & Ci.nsIWebProgressListener.STATE_TRANSFERRING))
            return;

        if (!this._pwmgr._remember)
            return;

        var domWin = aWebProgress.DOMWindow;
        var domDoc = domWin.document;

        // Only process things which might have HTML forms.
        if (!(domDoc instanceof Ci.nsIDOMHTMLDocument))
            return;

        this._pwmgr.log("onStateChange accepted: req = " +
                        (aRequest ?  aRequest.name : "(null)") +
                        ", flags = 0x" + aStateFlags.toString(16));

        // Fastback doesn't fire DOMContentLoaded, so process forms now.
        if (aStateFlags & Ci.nsIWebProgressListener.STATE_RESTORING) {
            this._pwmgr.log("onStateChange: restoring document");
            return this._pwmgr._fillDocument(domDoc);
        }

        // Add event listener to process page when DOM is complete.
        domDoc.addEventListener("DOMContentLoaded",
                                this._domEventListener, false);
        return;
    },

    // stubs for the nsIWebProgressListener interfaces which we don't use.
    onProgressChange : function() { throw "Unexpected onProgressChange"; },
    onLocationChange : function() { throw "Unexpected onLocationChange"; },
    onStatusChange   : function() { throw "Unexpected onStatusChange";   },
    onSecurityChange : function() { throw "Unexpected onSecurityChange"; }
},

I've tried commenting out/deleting whole portions of the file, only to have the error re-appear.

Any help would be totally.

Were you trying to "View Selection Source" when this error happened? I recently was having this same issue (with no noticeably problematic side-effects) and this blog post (May 2009) seems to be relevant. Looks like it's an error within Firefox that Firebug is just picking up in its console.

Although my error was on line 328 of nsLoginManager (Firefox 3.5.9), it was for the same problem: Component returned failure code: 0x80004001 (NS_ERROR_NOT_IMPLEMENTED) [nsIRequest.name]