--- a/toolkit/components/extensions/.eslintrc.js
+++ b/toolkit/components/extensions/.eslintrc.js
@@ -4,16 +4,18 @@ module.exports = {
 
   "globals": {
     "Cc": true,
     "Ci": true,
     "Cr": true,
     "Cu": true,
     "TextDecoder": false,
     "TextEncoder": false,
+
+    "MatchGlob": false,
     // Specific to WebExtensions:
     "AppConstants": true,
     "Extension": true,
     "ExtensionAPI": true,
     "ExtensionManagement": true,
     "ExtensionUtils": true,
     "extensions": true,
     "getContainerForCookieStoreId": true,

--- a/toolkit/components/extensions/Extension.jsm
+++ b/toolkit/components/extensions/Extension.jsm
@@ -57,18 +57,16 @@ XPCOMUtils.defineLazyModuleGetter(this, 
 XPCOMUtils.defineLazyModuleGetter(this, "ExtensionStorage",
                                   "resource://gre/modules/ExtensionStorage.jsm");
 XPCOMUtils.defineLazyModuleGetter(this, "ExtensionTestCommon",
                                   "resource://testing-common/ExtensionTestCommon.jsm");
 XPCOMUtils.defineLazyModuleGetter(this, "Locale",
                                   "resource://gre/modules/Locale.jsm");
 XPCOMUtils.defineLazyModuleGetter(this, "Log",
                                   "resource://gre/modules/Log.jsm");
-XPCOMUtils.defineLazyModuleGetter(this, "MatchGlobs",
-                                  "resource://gre/modules/MatchPattern.jsm");
 XPCOMUtils.defineLazyModuleGetter(this, "MatchPattern",
                                   "resource://gre/modules/MatchPattern.jsm");
 XPCOMUtils.defineLazyModuleGetter(this, "MessageChannel",
                                   "resource://gre/modules/MessageChannel.jsm");
 XPCOMUtils.defineLazyModuleGetter(this, "NetUtil",
                                   "resource://gre/modules/NetUtil.jsm");
 XPCOMUtils.defineLazyModuleGetter(this, "OS",
                                   "resource://gre/modules/osfile.jsm");
@@ -852,17 +850,17 @@ this.Extension = class extends Extension
     return {
       id: this.id,
       uuid: this.uuid,
       instanceId: this.instanceId,
       manifest: this.manifest,
       resourceURL: this.addonData.resourceURI.spec,
       baseURL: this.baseURI.spec,
       content_scripts: this.manifest.content_scripts || [],  // eslint-disable-line camelcase
-      webAccessibleResources: this.webAccessibleResources.serialize(),
+      webAccessibleResources: this.webAccessibleResources.map(res => res.glob),
       whiteListedHosts: this.whiteListedHosts.serialize(),
       localeData: this.localeData.serialize(),
       permissions: this.permissions,
       principal: this.principal,
       optionalPermissions: this.manifest.optional_permissions,
     };
   }
 
@@ -896,23 +894,22 @@ this.Extension = class extends Extension
       Services.obs.addObserver(observer, "message-manager-close");
       Services.obs.addObserver(observer, "message-manager-disconnect");
 
       ppmm.broadcastAsyncMessage(msg, data);
     });
   }
 
   runManifest(manifest) {
-    // Strip leading slashes from web_accessible_resources.
-    let strippedWebAccessibleResources = [];
+    let resources = [];
     if (manifest.web_accessible_resources) {
-      strippedWebAccessibleResources = manifest.web_accessible_resources.map(path => path.replace(/^\/+/, ""));
+      resources = manifest.web_accessible_resources.map(path => path.replace(/^\/*/, "/"));
     }
 
-    this.webAccessibleResources = new MatchGlobs(strippedWebAccessibleResources);
+    this.webAccessibleResources = resources.map(res => new MatchGlob(res));
 
     let promises = [];
     for (let directive in manifest) {
       if (manifest[directive] !== null) {
         promises.push(Management.emit(`manifest_${directive}`, directive, this, manifest));
 
         promises.push(Management.asyncEmitManifestEntry(this, directive));
       }

--- a/toolkit/components/extensions/ExtensionChild.jsm
+++ b/toolkit/components/extensions/ExtensionChild.jsm
@@ -21,18 +21,16 @@ const Cc = Components.classes;
 const Cu = Components.utils;
 const Cr = Components.results;
 
 Cu.import("resource://gre/modules/Services.jsm");
 Cu.import("resource://gre/modules/XPCOMUtils.jsm");
 
 XPCOMUtils.defineLazyModuleGetter(this, "ExtensionContent",
                                   "resource://gre/modules/ExtensionContent.jsm");
-XPCOMUtils.defineLazyModuleGetter(this, "MatchGlobs",
-                                  "resource://gre/modules/MatchPattern.jsm");
 XPCOMUtils.defineLazyModuleGetter(this, "MatchPattern",
                                   "resource://gre/modules/MatchPattern.jsm");
 XPCOMUtils.defineLazyModuleGetter(this, "MessageChannel",
                                   "resource://gre/modules/MessageChannel.jsm");
 XPCOMUtils.defineLazyModuleGetter(this, "NativeApp",
                                   "resource://gre/modules/NativeMessaging.jsm");
 XPCOMUtils.defineLazyModuleGetter(this, "PromiseUtils",
                                   "resource://gre/modules/PromiseUtils.jsm");
@@ -478,17 +476,17 @@ class BrowserExtensionContent extends Ev
 
     this.MESSAGE_EMIT_EVENT = `Extension:EmitEvent:${this.instanceId}`;
     Services.cpmm.addMessageListener(this.MESSAGE_EMIT_EVENT, this);
 
     defineLazyGetter(this, "scripts", () => {
       return data.content_scripts.map(scriptData => new ExtensionContent.Script(this, scriptData));
     });
 
-    this.webAccessibleResources = new MatchGlobs(data.webAccessibleResources);
+    this.webAccessibleResources = data.webAccessibleResources.map(res => new MatchGlob(res));
     this.whiteListedHosts = new MatchPattern(data.whiteListedHosts);
     this.permissions = data.permissions;
     this.optionalPermissions = data.optionalPermissions;
     this.principal = data.principal;
 
     this.localeData = new LocaleData(data.localeData);
 
     this.manifest = data.manifest;

--- a/toolkit/components/extensions/ExtensionManagement.jsm
+++ b/toolkit/components/extensions/ExtensionManagement.jsm
@@ -133,20 +133,17 @@ var Service = {
   extensionURILoadableByAnyone(uri) {
     let uuid = uri.host;
     let extension = this.uuidMap.get(uuid);
     if (!extension || !extension.webAccessibleResources) {
       return false;
     }
 
     let path = uri.QueryInterface(Ci.nsIURL).filePath;
-    if (path.length > 0 && path[0] == "/") {
-      path = path.substr(1);
-    }
-    return extension.webAccessibleResources.matches(path);
+    return extension.webAccessibleResources.some(res => res.matches(path));
   },
 
   // Checks whether a given extension can load this URI (typically via
   // an XML HTTP request). The manifest.json |permissions| directive
   // determines this.
   checkAddonMayLoad(extension, uri, explicit = false) {
     return extension.whiteListedHosts.matchesIgnoringPath(uri, explicit);
   },