--- a/toolkit/components/extensions/Extension.jsm
+++ b/toolkit/components/extensions/Extension.jsm
@@ -377,17 +377,17 @@ this.ExtensionData = class {
     if (!this.uuid) {
       this.uuid = UUIDMap.get(this.id);
     }
     return `moz-extension://${this.uuid}/${path}`;
   }
 
   async readDirectory(path) {
     if (this.rootURI instanceof Ci.nsIFileURL) {
-      let uri = Services.io.newURI(this.rootURI.resolve("./" + path));
+      let uri = Services.io.newURI("./" + path, null, this.rootURI);
       let fullPath = uri.QueryInterface(Ci.nsIFileURL).file.path;
 
       let iter = new OS.File.DirectoryIterator(fullPath);
       let results = [];
 
       try {
         await iter.forEach(entry => {
           results.push(entry);

--- a/toolkit/components/extensions/ext-cookies.js
+++ b/toolkit/components/extensions/ext-cookies.js
@@ -167,25 +167,25 @@ const query = function* (detailsIn, prop
   if (isPrivate) {
     storeId = PRIVATE_STORE;
   } else if ("storeId" in details) {
     storeId = details.storeId;
   }
 
   // We can use getCookiesFromHost for faster searching.
   let enumerator;
-  let uri;
+  let url;
   let originAttributes = {
     userContextId,
     privateBrowsingId: isPrivate ? 1 : 0,
   };
   if ("url" in details) {
     try {
-      uri = Services.io.newURI(details.url).QueryInterface(Ci.nsIURL);
-      enumerator = Services.cookies.getCookiesFromHost(uri.host, originAttributes);
+      url = new URL(details.url);
+      enumerator = Services.cookies.getCookiesFromHost(url.host, originAttributes);
     } catch (ex) {
       // This often happens for about: URLs
       return;
     }
   } else if ("domain" in details) {
     enumerator = Services.cookies.getCookiesFromHost(details.domain, originAttributes);
   } else {
     enumerator = Services.cookies.getCookiesWithOriginAttributes(JSON.stringify(originAttributes));
@@ -206,31 +206,30 @@ const query = function* (detailsIn, prop
 
       // path == cookiePath, but without the redundant string compare.
       if (path.length == cookiePath.length) {
         return true;
       }
 
       // URL path is a substring of the cookie path, so it matches if, and
       // only if, the next character is a path delimiter.
-      let pathDelimiters = ["/", "?", "#", ";"];
-      return pathDelimiters.includes(path[cookiePath.length]);
+      return path[cookiePath.length] === "/";
     }
 
     // "Restricts the retrieved cookies to those that would match the given URL."
-    if (uri) {
-      if (!domainMatches(uri.host)) {
+    if (url) {
+      if (!domainMatches(url.host)) {
         return false;
       }
 
-      if (cookie.isSecure && uri.scheme != "https") {
+      if (cookie.isSecure && url.protocol != "https:") {
         return false;
       }
 
-      if (!pathMatches(uri.pathQueryRef)) {
+      if (!pathMatches(url.path)) {
         return false;
       }
     }
 
     if ("name" in details && details.name != cookie.name) {
       return false;
     }
 
@@ -285,27 +284,27 @@ this.cookies = class extends ExtensionAP
         getAll: function(details) {
           let allowed = ["url", "name", "domain", "path", "secure", "session", "storeId"];
           let result = Array.from(query(details, allowed, context), convertCookie);
 
           return Promise.resolve(result);
         },
 
         set: function(details) {
-          let uri = Services.io.newURI(details.url).QueryInterface(Ci.nsIURL);
+          let uri = Services.io.newURI(details.url);
 
           let path;
           if (details.path !== null) {
             path = details.path;
           } else {
             // This interface essentially emulates the behavior of the
             // Set-Cookie header. In the case of an omitted path, the cookie
             // service uses the directory path of the requesting URL, ignoring
             // any filename or query parameters.
-            path = uri.directory;
+            path = uri.QueryInterface(Ci.nsIURL).directory;
           }
 
           let name = details.name !== null ? details.name : "";
           let value = details.value !== null ? details.value : "";
           let secure = details.secure !== null ? details.secure : false;
           let httpOnly = details.httpOnly !== null ? details.httpOnly : false;
           let isSession = details.expirationDate === null;
           let expiry = isSession ? Number.MAX_SAFE_INTEGER : details.expirationDate;

--- a/toolkit/components/extensions/ext-runtime.js
+++ b/toolkit/components/extensions/ext-runtime.js
@@ -119,22 +119,22 @@ this.runtime = class extends ExtensionAP
 
         setUninstallURL: function(url) {
           if (url.length == 0) {
             return Promise.resolve();
           }
 
           let uri;
           try {
-            uri = Services.io.newURI(url);
+            uri = new URL(url);
           } catch (e) {
             return Promise.reject({message: `Invalid URL: ${JSON.stringify(url)}`});
           }
 
-          if (uri.scheme != "http" && uri.scheme != "https") {
+          if (uri.protocol != "http:" && uri.protocol != "https:") {
             return Promise.reject({message: "url must have the scheme http or https"});
           }
 
           extension.uninstallURL = url;
           return Promise.resolve();
         },
       },
     };

--- a/toolkit/components/extensions/ext-toolkit.js
+++ b/toolkit/components/extensions/ext-toolkit.js
@@ -10,16 +10,18 @@
           getContainerForCookieStoreId: false,
           isValidCookieStoreId:false, isContainerCookieStoreId:false,
           isDefaultCookieStoreId: false, isPrivateCookieStoreId:false,
           EventManager: false, InputEventManager: false */
 
 XPCOMUtils.defineLazyModuleGetter(this, "ContextualIdentityService",
                                   "resource://gre/modules/ContextualIdentityService.jsm");
 
+Cu.importGlobalProperties(["URL"]);
+
 Cu.import("resource://gre/modules/ExtensionCommon.jsm");
 
 global.EventEmitter = ExtensionUtils.EventEmitter;
 global.EventManager = ExtensionCommon.EventManager;
 global.InputEventManager = class extends EventManager {
   constructor(...args) {
     super(...args);
     this.inputHandling = true;