Detect and handle Firebug related problems.

* Check for `chromeWin.Firebug`.
* Check for an undefined `fbContext`.

Intentionally leave logging in place, so that if error cases have been
missed (or appear), they are noticed in the future.

Signed-off-by: Johan Sundström <oyasumi+github@gmail.com>

components/greasemonkey.js

@@ -380,13 +380,23 @@ var greasemonkeyService = {
   },
 
   getFirebugConsole: function(unsafeContentWin, chromeWin) {
+    // If we can't find this object, there's no chance the rest of this
+    // function will work.
+    if ('undefined'==typeof chromeWin.Firebug) return null;
+
     try {
       chromeWin = chromeWin.top;
       var fbVersion = parseFloat(chromeWin.Firebug.version, 10);
       var fbConsole = chromeWin.Firebug.Console;
       var fbContext = chromeWin.TabWatcher &&
         chromeWin.TabWatcher.getContextByWindow(unsafeContentWin);
 
+      // Firebug 1.4 will give no context, when disabled for the current site.
+      // We can't run that way.
+      if ('undefined'==typeof fbContext) {
+        return null;
+      }
+
       function findActiveContext() {
         for (var i=0; i<fbContext.activeConsoleHandlers.length; i++) {
           if (fbContext.activeConsoleHandlers[i].window == unsafeContentWin) {
@@ -437,8 +447,6 @@ var greasemonkeyService = {
 
 greasemonkeyService.wrappedJSObject = greasemonkeyService;
 
-//loggify(greasemonkeyService, "greasemonkeyService");
-
 
 
 /**