--- a/addon-sdk/source/test/addons/embedded-webextension/main.js
+++ b/addon-sdk/source/test/addons/embedded-webextension/main.js
@@ -130,17 +130,17 @@ exports.testEmbeddedWebExtensionContentS
         port.onDisconnect.addListener(() => {
           assert.equal(numExpectedMessages, 0, "Got the epected number of port messages");
           resolve();
         });
       };
       browser.runtime.onConnect.addListener(portListener);
     });
 
-    let url = "data:text/html;charset=utf-8,<h1>Test Page</h1>";
+    let url = "http://example.org/";
 
     var openedTab;
     tabs.once('open', function onOpen(tab) {
       openedTab = tab;
     });
     tabs.open(url);
 
     yield Promise.all([

--- a/toolkit/components/extensions/ExtensionContent.jsm
+++ b/toolkit/components/extensions/ExtensionContent.jsm
@@ -138,33 +138,43 @@ Script.prototype = {
       urls.push(url);
     }
 
     return urls;
   },
 
   matches(window) {
     let uri = window.document.documentURIObject;
+    let principal = window.document.nodePrincipal;
 
     // If mozAddonManager is present on this page, don't allow
     // content scripts.
     if (window.navigator.mozAddonManager !== undefined) {
       return false;
     }
 
-    if (this.match_about_blank && ["about:blank", "about:srcdoc"].includes(uri.spec)) {
-      const principal = window.document.nodePrincipal;
-
+    if (this.match_about_blank) {
       // When matching top-level about:blank documents,
       // allow loading into any with a NullPrincipal.
-      if (window === window.top && principal.isNullPrincipal) {
+      if (uri.spec === "about:blank" && window === window.top && principal.isNullPrincipal) {
         return true;
       }
+
       // When matching about:blank/srcdoc iframes, the checks below
       // need to be performed against the "owner" document's URI.
+      if (["about:blank", "about:srcdoc"].includes(uri.spec)) {
+        uri = principal.URI;
+      }
+    }
+
+    // Documents from data: URIs also inherit the principal.
+    if (Services.netUtils.URIChainHasFlags(uri, Ci.nsIProtocolHandler.URI_INHERITS_SECURITY_CONTEXT)) {
+      if (!this.match_about_blank) {
+        return false;
+      }
       uri = principal.URI;
     }
 
     if (!(this.matches_.matches(uri) || this.matches_host_.matchesIgnoringPath(uri))) {
       return false;
     }
 
     if (this.exclude_matches_.matches(uri)) {