As part of fixing bug 453442, gavin brought this up in review: > It probably makes more sense long term to have shouldLoadFavIcon take an > optional <browser> argument (defaulting to the tabbrowser's selectedBrowser) so > that callers don't have to worry about the distinction. Could also turn that > ("schemeIs" in aURI) check into an instanceof check while we're at it! > Followup? "The distinction" in question is that between document.location and document.documentURIObject. The fix to bug 453442 involved changing from one to the other, to detect the case where we are showing an error page (where document.location will show the page's url, not the about: URL of the error page itself).