diff --git a/browser/components/downloads/test/browser/browser_overflow_anchor.js b/browser/components/downloads/test/browser/browser_overflow_anchor.js
index 595b2ebc316d..63387314eabf 100644
--- a/browser/components/downloads/test/browser/browser_overflow_anchor.js
+++ b/browser/components/downloads/test/browser/browser_overflow_anchor.js
@@ -98,11 +98,11 @@ function unlockWidth(aItemIDs) {
  * @param aIsOverflowed if we're waiting for the item to be overflowed.
  */
 function waitForOverflowed(aItem, aIsOverflowed) {
-  return new Promise(resolve => {
-    if (aItem.overflowed == aIsOverflowed) {
-      return resolve();
-    }
+  if (aItem.overflowed == aIsOverflowed) {
+    return Promise.resolve();
+  }
 
+  return new Promise(resolve => {
     let observer = new MutationObserver(function(aMutations) {
       if (aItem.overflowed == aIsOverflowed) {
         observer.disconnect();
@@ -110,6 +110,5 @@ function waitForOverflowed(aItem, aIsOverflowed) {
       }
     });
     observer.observe(aItem.node, {attributes: true});
-
   });
 }
diff --git a/browser/components/downloads/test/browser/head.js b/browser/components/downloads/test/browser/head.js
index d86a87fda880..c24b729c6e26 100644
--- a/browser/components/downloads/test/browser/head.js
+++ b/browser/components/downloads/test/browser/head.js
@@ -113,11 +113,11 @@ function promiseFocus() {
 }
 
 function promisePanelOpened() {
-  return new Promise(resolve => {
+  if (DownloadsPanel.panel && DownloadsPanel.panel.state == "open") {
+    return Promise.resolve();
+  }
 
-    if (DownloadsPanel.panel && DownloadsPanel.panel.state == "open") {
-      return resolve();
-    }
+  return new Promise(resolve => {
 
     // Hook to wait until the panel is shown.
     let originalOnPopupShown = DownloadsPanel.onPopupShown;
diff --git a/browser/experiments/Experiments.jsm b/browser/experiments/Experiments.jsm
index ce38c84164ee..4129bc42923c 100644
--- a/browser/experiments/Experiments.jsm
+++ b/browser/experiments/Experiments.jsm
@@ -969,7 +969,7 @@ Experiments.Experiments.prototype = {
         xhr.send(null);
       } catch (e) {
         this._log.error("httpGetRequest() - Error opening request to " + url + ": " + e);
-        return Promise.reject(new Error("Experiments - Error opening XHR for " + url));
+        reject(new Error("Experiments - Error opening XHR for " + url));
       }
     });
   },
diff --git a/browser/modules/ContentSearch.jsm b/browser/modules/ContentSearch.jsm
index 3f4fd2f4d755..786c3b02d2f9 100644
--- a/browser/modules/ContentSearch.jsm
+++ b/browser/modules/ContentSearch.jsm
@@ -533,7 +533,7 @@ this.ContentSearch = {
         // This throws if the URI is erroneously encoded.
         xhr.send();
       } catch (err) {
-        return Promise.resolve(null);
+        resolve(null);
       }
     });
   },
diff --git a/browser/modules/test/browser/browser_ContentSearch.js b/browser/modules/test/browser/browser_ContentSearch.js
index c37923e6713a..4946b13852f9 100644
--- a/browser/modules/test/browser/browser_ContentSearch.js
+++ b/browser/modules/test/browser/browser_ContentSearch.js
@@ -410,7 +410,7 @@ function arrayBufferFromDataURI(uri) {
     try {
       xhr.send();
     } catch (err) {
-      return Promise.resolve(null);
+      resolve(null);
     }
   });
 }