Issue 5864 - Remove previous style sheet before adding one

lib/cssInjection.js

Index: lib/cssInjection.js
===================================================================
--- a/lib/cssInjection.js
+++ b/lib/cssInjection.js
@@ -25,33 +25,48 @@
 const {checkWhitelisted} = require("whitelisting");
 const {extractHostFromFrame} = require("url");
 const {port} = require("messaging");
 const devtools = require("devtools");
 
 const userStyleSheetsSupported = "extensionTypes" in chrome &&
                                  "CSSOrigin" in chrome.extensionTypes;
 
-function hideElements(tabId, frameId, selectors)
+function convertSelectors(selectors)
+{
+  return selectors.join(", ") + "{display: none !important;}";
+}
+
+function addStyleSheet(tabId, frameId, selectors)
 {
   chrome.tabs.insertCSS(tabId, {
-    code: selectors.join(", ") + "{display: none !important;}",
+    code: convertSelectors(selectors),
     cssOrigin: "user",
     frameId,
     matchAboutBlank: true,
     runAt: "document_start"
   });
 }
 
-port.on("elemhide.getSelectors", (msg, sender) =>
+function removeStyleSheet(tabId, frameId, selectors)
+{
+  chrome.tabs.removeCSS(tabId, {
+    code: convertSelectors(selectors),
+    cssOrigin: "user",
+    frameId,
+    matchAboutBlank: true
+  });
+}
+
+port.on("elemhide.getSelectors", (message, sender) =>
 {
   let selectors = [];
   let emulatedPatterns = [];
   let trace = devtools && devtools.hasPanel(sender.page);
-  let inject = !userStyleSheetsSupported;
+  let inline = !userStyleSheetsSupported;
 
   if (!checkWhitelisted(sender.page, sender.frame,
                         RegExpFilter.typeMap.DOCUMENT |
                         RegExpFilter.typeMap.ELEMHIDE))
   {
     let hostname = extractHostFromFrame(sender.frame);
     let specificOnly = checkWhitelisted(sender.page, sender.frame,
                                         RegExpFilter.typeMap.GENERICHIDE);
@@ -60,22 +75,26 @@
       hostname,
       specificOnly ? ElemHide.SPECIFIC_ONLY : ElemHide.ALL_MATCHING
     );
 
     for (let filter of ElemHideEmulation.getRulesForDomain(hostname))
       emulatedPatterns.push({selector: filter.selector, text: filter.text});
   }
 
-  if (!inject && selectors.length > 0)
-    hideElements(sender.page.id, sender.frame.id, selectors);
+  if (!inline && selectors.length > 0)
+    addStyleSheet(sender.page.id, sender.frame.id, selectors);
 
-  let response = {trace, inject, emulatedPatterns};
-  if (trace || inject)
+  let response = {trace, inline, emulatedPatterns};
+  if (trace || inline)
     response.selectors = selectors;
 
   return response;
 });
 
-port.on("elemhide.injectSelectors", (msg, sender) =>
+port.on("elemhide.injectSelectors", (message, sender) =>
 {
-  hideElements(sender.page.id, sender.frame.id, msg.selectors);
+  if (message.oldSelectors.length > 0)
+    removeStyleSheet(sender.page.id, sender.frame.id, message.oldSelectors);
+
+  if (message.selectors.length > 0)
+    addStyleSheet(sender.page.id, sender.frame.id, message.selectors);
 });