--- a/browser/components/contextualidentity/test/browser/browser_aboutURLs.js
+++ b/browser/components/contextualidentity/test/browser/browser_aboutURLs.js
@@ -2,41 +2,37 @@
 
 // For some about: URLs, they will take more time to load and cause timeout.
 // See Bug 1270998.
 requestLongerTimeout(2);
 
 add_task(async function() {
   let aboutURLs = [];
 
-  // List of about: URLs that may cause problem, so we skip them in this test.
-  let skipURLs = [
-    // about:credits will initiate network request.
+  // List of about: URLs that will initiate network requests.
+  let networkURLs = [
     "credits",
-    // about:telemetry will fetch Telemetry asynchronously and takes longer,
-    // so we skip this for now.
-    "telemetry",
-    // about:downloads causes a shutdown leak with stylo-chrome. bug 1419943.
-    "downloads"
+    "telemetry" // about:telemetry will fetch Telemetry asynchrounously and takes
+                // longer, we skip this for now.
   ];
 
   for (let cid in Cc) {
     let result = cid.match(/@mozilla.org\/network\/protocol\/about;1\?what\=(.*)$/);
     if (!result) {
       continue;
     }
 
     let aboutType = result[1];
     let contract = "@mozilla.org/network/protocol/about;1?what=" + aboutType;
     try {
       let am = Cc[contract].getService(Ci.nsIAboutModule);
       let uri = Services.io.newURI("about:" + aboutType);
       let flags = am.getURIFlags(uri);
       if (!(flags & Ci.nsIAboutModule.HIDE_FROM_ABOUTABOUT) &&
-          !skipURLs.includes(aboutType)) {
+          !networkURLs.includes(aboutType)) {
         aboutURLs.push(aboutType);
       }
     } catch (e) {
       // getService might have thrown if the component doesn't actually
       // implement nsIAboutModule
     }
   }
 

--- a/modules/libpref/init/all.js
+++ b/modules/libpref/init/all.js
@@ -5850,18 +5850,22 @@ pref("media.block-autoplay-until-in-fore
 pref("layout.css.servo.enabled", true);
 #else
 pref("layout.css.servo.enabled", false);
 #endif
 // Whether Stylo is enabled for chrome document?
 // If Stylo is not enabled, this pref doesn't take any effect.
 // Note that this pref is only read once when requested. Changing it
 // at runtime may have no effect.
+#ifdef MOZ_OLD_STYLE
+pref("layout.css.servo.chrome.enabled", false);
+#else
 pref("layout.css.servo.chrome.enabled", true);
 #endif
+#endif
 
 // TODO: Bug 1324406: Treat 'data:' documents as unique, opaque origins
 // If true, data: URIs will be treated as unique opaque origins, hence will use
 // a NullPrincipal as the security context.
 // Otherwise it will inherit the origin from parent node, this is the legacy
 // behavior of Firefox.
 pref("security.data_uri.unique_opaque_origin", true);