diff --git a/src/js/messaging.js b/src/js/messaging.js
index 4021fe5d4..0b778394c 100644
--- a/src/js/messaging.js
+++ b/src/js/messaging.js
@@ -627,7 +627,13 @@ const retrieveContentScriptParameters = function(sender, request) {
     response.specificCosmeticFilters =
         µb.cosmeticFilteringEngine.retrieveSpecificSelectors(request, response);
 
-    if ( µb.canInjectScriptletsNow === false ) {
+    // https://github.com/uBlockOrigin/uBlock-issues/issues/688#issuecomment-748179731
+    //   For non-network URIs, scriptlet injection is deferred to here. The
+    //   effective URL is available here in `request.url`.
+    if (
+        µb.canInjectScriptletsNow === false ||
+        µb.URI.isNetworkURI(sender.frameURL) === false
+    ) {
         response.scriptlets = µb.scriptletFilteringEngine.retrieve(request);
     }
 
diff --git a/src/js/scriptlet-filtering.js b/src/js/scriptlet-filtering.js
index a03e4a04f..39b38396b 100644
--- a/src/js/scriptlet-filtering.js
+++ b/src/js/scriptlet-filtering.js
@@ -377,7 +377,6 @@
 
     api.injectNow = function(details) {
         if ( typeof details.frameId !== 'number' ) { return; }
-        if ( µb.URI.isNetworkURI(details.url) === false ) { return; }
         const request = {
             tabId: details.tabId,
             frameId: details.frameId,
diff --git a/src/js/tab.js b/src/js/tab.js
index cc09eb7bb..3f70aec0e 100644
--- a/src/js/tab.js
+++ b/src/js/tab.js
@@ -868,7 +868,10 @@ vAPI.Tabs = class extends vAPI.Tabs {
     // properly setup if network requests are fired from within the tab.
     // Example: Chromium + case #6 at
     //          http://raymondhill.net/ublock/popup.html
-
+    // https://github.com/uBlockOrigin/uBlock-issues/issues/688#issuecomment-748179731
+    //   For non-network URIs, defer scriptlet injection to content script. The
+    //   reason for this is that we need the effective URL and this information
+    //   is not available at this point.
     onNavigation(details) {
         super.onNavigation(details);
         const µb = µBlock;
@@ -879,8 +882,8 @@ vAPI.Tabs = class extends vAPI.Tabs {
                 pageStore.journalAddRootFrame('committed', details.url);
             }
         }
-        if ( µb.canInjectScriptletsNow ) {
-            let pageStore = µb.pageStoreFromTabId(details.tabId);
+        if ( µb.canInjectScriptletsNow && µb.URI.isNetworkURI(details.url) ) {
+            const pageStore = µb.pageStoreFromTabId(details.tabId);
             if ( pageStore !== null && pageStore.getNetFilteringSwitch() ) {
                 µb.scriptletFilteringEngine.injectNow(details);
             }