FF: ensure styles are applied to about:blank iframes

fixes #215

background/background.js

@@ -64,6 +64,12 @@ chrome.runtime.onMessage.addListener(onRuntimeMessage);
         {hostSuffix: '.githubusercontent.com', urlSuffix: '.user.styl'},
       ]
     });
+    // FF misses some about:blank iframes so we inject our content script explicitly
+    chrome.webNavigation.onDOMContentLoaded.addListener(webNavIframeHelperFF, {
+      url: [
+        {urlEquals: 'about:blank'},
+      ]
+    });
   }
 }
 
@@ -330,6 +336,20 @@ function webNavUsercssInstallerFF(data) {
 }
 
 
+function webNavIframeHelperFF({tabId, frameId}) {
+  if (!frameId) return;
+  sendMessage({method: 'ping', tabId, frameId}, pong => {
+    ignoreChromeError();
+    if (pong) return;
+    chrome.tabs.executeScript(tabId, {
+      frameId,
+      file: '/content/apply.js',
+      matchAboutBlank: true,
+    }, ignoreChromeError);
+  });
+}
+
+
 function updateIcon({tab, styles}) {
   if (tab.id < 0) {
     return;