diff --git a/toolkit/components/antitracking/AntiTrackingCommon.cpp b/toolkit/components/antitracking/AntiTrackingCommon.cpp
index 6cdb94137afa..b1b3d967ef92 100644
--- a/toolkit/components/antitracking/AntiTrackingCommon.cpp
+++ b/toolkit/components/antitracking/AntiTrackingCommon.cpp
@@ -220,10 +220,7 @@ int32_t CookiesBehavior(nsILoadInfo* aLoadInfo,
 
   // WebExtensions 3rd party URI always get BEHAVIOR_ACCEPT as cookieBehavior,
   // this is semantically equivalent to the principal having a AddonPolicy().
-  bool is3rdPartyMozExt = false;
-  if (NS_SUCCEEDED(
-          a3rdPartyURI->SchemeIs("moz-extension", &is3rdPartyMozExt)) &&
-      is3rdPartyMozExt) {
+  if (a3rdPartyURI->SchemeIs("moz-extension")) {
     return nsICookieService::BEHAVIOR_ACCEPT;
   }
 
diff --git a/toolkit/components/antitracking/StorageAccess.cpp b/toolkit/components/antitracking/StorageAccess.cpp
index a9f6c89088d2..e4b19e8937dc 100644
--- a/toolkit/components/antitracking/StorageAccess.cpp
+++ b/toolkit/components/antitracking/StorageAccess.cpp
@@ -138,12 +138,8 @@ static StorageAccess InternalStorageAllowedCheck(
   if (!uri) {
     Unused << aPrincipal->GetURI(getter_AddRefs(uri));
   }
-  if (uri) {
-    bool isAbout = false;
-    MOZ_ALWAYS_SUCCEEDS(uri->SchemeIs("about", &isAbout));
-    if (isAbout) {
-      return access;
-    }
+  if (uri && uri->SchemeIs("about")) {
+    return access;
   }
 
   if (!StorageDisabledByAntiTracking(aWindow, aChannel, aPrincipal, aURI,
diff --git a/toolkit/components/places/nsNavBookmarks.cpp b/toolkit/components/places/nsNavBookmarks.cpp
index dc1f0ac9ddee..6f1efe388054 100644
--- a/toolkit/components/places/nsNavBookmarks.cpp
+++ b/toolkit/components/places/nsNavBookmarks.cpp
@@ -1919,10 +1919,7 @@ nsNavBookmarks::OnPageChanged(nsIURI* aURI, uint32_t aChangedAttribute,
     changeData.bookmark.type = TYPE_BOOKMARK;
 
     // Favicons may be set to either pure URIs or to folder URIs
-    bool isPlaceURI;
-    rv = aURI->SchemeIs("place", &isPlaceURI);
-    NS_ENSURE_SUCCESS(rv, rv);
-    if (isPlaceURI) {
+    if (aURI->SchemeIs("place")) {
       nsNavHistory* history = nsNavHistory::GetHistoryService();
       NS_ENSURE_TRUE(history, NS_ERROR_OUT_OF_MEMORY);
 
diff --git a/toolkit/components/url-classifier/nsUrlClassifierStreamUpdater.cpp b/toolkit/components/url-classifier/nsUrlClassifierStreamUpdater.cpp
index 173d4ce55e98..0e19a54a8664 100644
--- a/toolkit/components/url-classifier/nsUrlClassifierStreamUpdater.cpp
+++ b/toolkit/components/url-classifier/nsUrlClassifierStreamUpdater.cpp
@@ -177,9 +177,7 @@ nsresult nsUrlClassifierStreamUpdater::FetchUpdate(
   // Set the appropriate content type for file/data URIs, for unit testing
   // purposes.
   // This is only used for testing and should be deleted.
-  bool match;
-  if ((NS_SUCCEEDED(aUpdateUrl->SchemeIs("file", &match)) && match) ||
-      (NS_SUCCEEDED(aUpdateUrl->SchemeIs("data", &match)) && match)) {
+  if (aUpdateUrl->SchemeIs("file") || aUpdateUrl->SchemeIs("data")) {
     mChannel->SetContentType(
         NS_LITERAL_CSTRING("application/vnd.google.safebrowsing-update"));
   } else {
diff --git a/toolkit/components/windowwatcher/nsWindowWatcher.cpp b/toolkit/components/windowwatcher/nsWindowWatcher.cpp
index 6e6b88db6a80..f6292f56f037 100644
--- a/toolkit/components/windowwatcher/nsWindowWatcher.cpp
+++ b/toolkit/components/windowwatcher/nsWindowWatcher.cpp
@@ -617,7 +617,7 @@ nsresult nsWindowWatcher::OpenWindowInternal(
     if (NS_FAILED(rv)) {
       return rv;
     }
-    uriToLoad->SchemeIs("chrome", &uriToLoadIsChrome);
+    uriToLoadIsChrome = uriToLoad->SchemeIs("chrome");
   }
 
   bool nameSpecified = false;
diff --git a/toolkit/mozapps/extensions/AddonContentPolicy.cpp b/toolkit/mozapps/extensions/AddonContentPolicy.cpp
index 705073cfde75..004c5ead134e 100644
--- a/toolkit/mozapps/extensions/AddonContentPolicy.cpp
+++ b/toolkit/mozapps/extensions/AddonContentPolicy.cpp
@@ -111,11 +111,8 @@ AddonContentPolicy::ShouldLoad(nsIURI* aContentLocation, nsILoadInfo* aLoadInfo,
 
   // Only apply this policy to requests from documents loaded from
   // moz-extension URLs, or to resources being loaded from moz-extension URLs.
-  bool equals;
-  if (!((NS_SUCCEEDED(aContentLocation->SchemeIs("moz-extension", &equals)) &&
-         equals) ||
-        (NS_SUCCEEDED(requestOrigin->SchemeIs("moz-extension", &equals)) &&
-         equals))) {
+  if (!(aContentLocation->SchemeIs("moz-extension") ||
+        requestOrigin->SchemeIs("moz-extension"))) {
     return NS_OK;
   }
 
diff --git a/toolkit/mozapps/extensions/AddonManagerWebAPI.cpp b/toolkit/mozapps/extensions/AddonManagerWebAPI.cpp
index 9c721ac315ca..8b44fdd29876 100644
--- a/toolkit/mozapps/extensions/AddonManagerWebAPI.cpp
+++ b/toolkit/mozapps/extensions/AddonManagerWebAPI.cpp
@@ -55,9 +55,7 @@ bool AddonManagerWebAPI::IsValidSite(nsIURI* uri) {
     return false;
   }
 
-  bool isSecure;
-  nsresult rv = uri->SchemeIs("https", &isSecure);
-  if (NS_FAILED(rv) || !isSecure) {
+  if (!uri->SchemeIs("https")) {
     if (!(xpc::IsInAutomation() &&
           Preferences::GetBool("extensions.webapi.testing.http", false))) {
       return false;
@@ -65,7 +63,7 @@ bool AddonManagerWebAPI::IsValidSite(nsIURI* uri) {
   }
 
   nsAutoCString host;
-  rv = uri->GetHost(host);
+  nsresult rv = uri->GetHost(host);
   if (NS_FAILED(rv)) {
     return false;
   }
diff --git a/toolkit/system/unixproxy/nsUnixSystemProxySettings.cpp b/toolkit/system/unixproxy/nsUnixSystemProxySettings.cpp
index f099193e630d..b28435919122 100644
--- a/toolkit/system/unixproxy/nsUnixSystemProxySettings.cpp
+++ b/toolkit/system/unixproxy/nsUnixSystemProxySettings.cpp
@@ -175,10 +175,9 @@ static nsresult GetProxyFromEnvironment(const nsACString& aScheme,
 
   // Is there a way to specify "socks://" or something in these environment
   // variables? I can't find any documentation.
-  bool isHTTP;
-  rv = proxyURI->SchemeIs("http", &isHTTP);
-  NS_ENSURE_SUCCESS(rv, rv);
-  if (!isHTTP) return NS_ERROR_UNKNOWN_PROTOCOL;
+  if (!proxyURI->SchemeIs("http")) {
+    return NS_ERROR_UNKNOWN_PROTOCOL;
+  }
 
   nsAutoCString proxyHost;
   rv = proxyURI->GetHost(proxyHost);
diff --git a/toolkit/xre/nsAppRunner.cpp b/toolkit/xre/nsAppRunner.cpp
index 7138fd94b8ac..bf8d5f5407a8 100644
--- a/toolkit/xre/nsAppRunner.cpp
+++ b/toolkit/xre/nsAppRunner.cpp
@@ -1001,18 +1001,13 @@ nsXULAppInfo::GetServerURL(nsIURL** aServerURL) {
 
 NS_IMETHODIMP
 nsXULAppInfo::SetServerURL(nsIURL* aServerURL) {
-  bool schemeOk;
-  // only allow https or http URLs
-  nsresult rv = aServerURL->SchemeIs("https", &schemeOk);
-  NS_ENSURE_SUCCESS(rv, rv);
-  if (!schemeOk) {
-    rv = aServerURL->SchemeIs("http", &schemeOk);
-    NS_ENSURE_SUCCESS(rv, rv);
-
-    if (!schemeOk) return NS_ERROR_INVALID_ARG;
+  // Only allow https or http URLs
+  if (!aServerURL->SchemeIs("http") && !aServerURL->SchemeIs("https")) {
+    return NS_ERROR_INVALID_ARG;
   }
+
   nsAutoCString spec;
-  rv = aServerURL->GetSpec(spec);
+  nsresult rv = aServerURL->GetSpec(spec);
   NS_ENSURE_SUCCESS(rv, rv);
 
   return CrashReporter::SetServerURL(spec);