diff --git a/background/background.js b/background/background.js
index 2cdbc06c..b3a31a92 100644
--- a/background/background.js
+++ b/background/background.js
@@ -175,6 +175,8 @@ msg.on((msg, sender) => {
 //#endregion
 
 Promise.all([
+  browser.extension.isAllowedFileSchemeAccess()
+    .then(res => API.data.set('hasFileAccess', res)),
   bgReady.styles,
   /* These are loaded conditionally.
      Each item uses `require` individually so IDE can jump to the source and track usage. */
diff --git a/background/update-manager.js b/background/update-manager.js
index 9797c115..0c84cef8 100644
--- a/background/update-manager.js
+++ b/background/update-manager.js
@@ -223,7 +223,9 @@ const updateMan = (() => {
       let err;
       if (!delta && !ignoreDigest) {
         // re-install is invalid in a soft upgrade
-        err = response === style.sourceCode ? STATES.SAME_CODE : STATES.SAME_VERSION;
+        err = response === style.sourceCode
+          ? STATES.SAME_CODE
+          : !URLS.isLocalhost(updateUrl) && STATES.SAME_VERSION;
       }
       if (delta < 0) {
         // downgrade is always invalid
diff --git a/install-usercss/install-usercss.js b/install-usercss/install-usercss.js
index 8c978a0d..2cc9a06a 100644
--- a/install-usercss/install-usercss.js
+++ b/install-usercss/install-usercss.js
@@ -1,6 +1,6 @@
 /* global $ $create $createLink $$remove showSpinner */// dom.js
 /* global API */// msg.js
-/* global closeCurrentTab deepEqual */// toolbox.js
+/* global URLS closeCurrentTab deepEqual */// toolbox.js
 /* global messageBox */
 /* global prefs */
 /* global preinit */
@@ -61,12 +61,18 @@ setTimeout(() => !cm && showSpinner($('#header')), 200);
     '/js/color/color-view',
   ]));
 
-  ({tabId, initialUrl} = await preinit);
+  ({tabId, initialUrl} = preinit);
   liveReload = initLiveReload();
 
-  const {dup, style, error, sourceCode} = await preinit.ready;
+  const [
+    {dup, style, error, sourceCode},
+    hasFileAccess,
+  ] = await Promise.all([
+    preinit.ready,
+    API.data.get('hasFileAccess'),
+  ]);
   if (!style && sourceCode == null) {
-    messageBox.alert(isNaN(error) ? error : 'HTTP Error ' + error, 'pre');
+    messageBox.alert(isNaN(error) ? `${error}` : 'HTTP Error ' + error, 'pre');
     return;
   }
   await scriptsReady;
@@ -118,7 +124,7 @@ setTimeout(() => !cm && showSpinner($('#header')), 200);
     checker.checked = true;
     // there is no way to "unset" updateUrl, you can only overwrite it.
     checker.disabled = true;
-  } else if (updateUrl.protocol !== 'file:') {
+  } else if (updateUrl.protocol !== 'file:' || hasFileAccess) {
     checker.checked = true;
     style.updateUrl = updateUrl.href;
   }
@@ -129,7 +135,7 @@ setTimeout(() => !cm && showSpinner($('#header')), 200);
   $('.set-update-url p').textContent = updateUrl.href.length < 300 ? updateUrl.href :
     updateUrl.href.slice(0, 300) + '...';
 
-  if (initialUrl.startsWith('file:')) {
+  if (URLS.isLocalhost(initialUrl)) {
     $('.live-reload input').onchange = liveReload.onToggled;
   } else {
     $('.live-reload').remove();
diff --git a/install-usercss/preinit.js b/install-usercss/preinit.js
index 6f37f2e0..8451e095 100644
--- a/install-usercss/preinit.js
+++ b/install-usercss/preinit.js
@@ -25,7 +25,10 @@ const preinit = (() => {
   function DirectDownloader() {
     let oldCode = null;
     return async () => {
-      const code = await download(initialUrl);
+      const code = await download(initialUrl, {
+        // Disabling cache on http://localhost otherwise the recheck delay gets too big
+        headers: {'Cache-Control': 'no-cache, no-store'},
+      });
       if (oldCode !== code) {
         oldCode = code;
         return code;
diff --git a/js/toolbox.js b/js/toolbox.js
index a5966342..a11ae1c0 100644
--- a/js/toolbox.js
+++ b/js/toolbox.js
@@ -115,6 +115,8 @@ const URLS = {
     url.startsWith(URLS.ownOrigin) ||
     !URLS.chromeProtectsNTP && url.startsWith('chrome://newtab/')
   ),
+
+  isLocalhost: url => /^file:|^https?:\/\/(localhost|127\.0\.0\.1)\//.test(url),
 };
 
 const RX_META = /\/\*!?\s*==userstyle==[\s\S]*?==\/userstyle==\s*\*\//i;