Issue 5864 - Remove previous style sheet before adding one

lib/cssInjection.js

Index: lib/cssInjection.js
===================================================================
--- a/lib/cssInjection.js
+++ b/lib/cssInjection.js
@@ -38,31 +38,31 @@
     frameId,
     matchAboutBlank: true,
     runAt: "document_start"
   });
 }
 
 function removeStyleSheet(tabId, frameId, styleSheet)
 {
-  chrome.tabs.removeCSS(tabId, {
+  browser.tabs.removeCSS(tabId, {
     code: styleSheet,
     cssOrigin: "user",
     frameId,
     matchAboutBlank: true
   });
 }
 
-function updateFrameStyles(pageId, frameId, selectors, groupName)
+function updateFrameStyles(tabId, frameId, selectors, groupName)
 {
   let styleSheet = null;
   if (selectors.length > 0)
     styleSheet = selectors.join(", ") + "{display: none !important;}";
 
-  let frame = ext.getFrame(pageId, frameId);
+  let frame = ext.getFrame(tabId, frameId);
   if (!frame.injectedStyleSheets)
     frame.injectedStyleSheets = new Map();
 
   let oldStyleSheet = frame.injectedStyleSheets.get(groupName);
 
   // Ideally we would compare the old and new style sheets and skip this code
   // if they're the same, but the old style sheet can be a leftover from a
   // previous instance of the frame. We must add the new style sheet