diff --git a/lib/builtin-rules.js b/lib/builtin-rules.js
index 0969997..7f7d068 100644
--- a/lib/builtin-rules.js
+++ b/lib/builtin-rules.js
@@ -33,7 +33,7 @@ d35aaqx5ub95lt.cloudfront.net/js/app-*.js$script
 ! --
 github.com
 gist.github.com
-    std-PerformanceObserver,std-queueMicrotask,gh-compat,gh-main-csp,sm-gh-extra,sm-cookie
+    std-PerformanceObserver,std-queueMicrotask,gh-compat,gh-turbo,gh-main-csp,sm-gh-extra,sm-cookie
 github.com/socket-worker.js$script
 gist.github.com/socket-worker.js$script
 github.com/assets-cdn/worker/socket-worker-*.js$script
diff --git a/lib/main.js b/lib/main.js
index f530672..345c1ad 100644
--- a/lib/main.js
+++ b/lib/main.js
@@ -97,6 +97,9 @@ function evaluateFix(fix, script, csp, contentReplace) {
             contentReplace.push([`this.matchFields?.join("-")`, `((y)=>y?y.join("-"):y)(this.matchFields)`]);
             contentReplace.push([`H.integrity=S.sriHashes[t],`, ``]);
             break;
+        case "gh-turbo":
+            script.push(pf.Github_disableTurbo);
+            break;
         case "gh-main-csp":
             csp["connect-src"] = ["objects.githubusercontent.com", "codeload.github.com"];
             break;
@@ -210,6 +213,14 @@ function supersededFixes(service) {
         superseded.add("google-regexp");
         superseded.add("notion-regexp");
     }
+    if (service.isWebComponentsSupported) {
+        superseded.add("gh-compat");
+        superseded.add("pkg-WebComponents");
+        superseded.add("std-ShadowDOM");
+    }
+    if (service.isLogicalAssignSupported) {
+        superseded.add("wordpress-logicalassign");
+    }
     return superseded;
 }
 
@@ -615,6 +626,21 @@ class MergedFix {
     }
 }
 
+const gWindowOpenListener = {
+    onOpenWindow: function(xulWindow)
+    {
+        const window = xulWindow.QueryInterface(Components.interfaces.nsIInterfaceRequestor)
+                                .getInterface(Components.interfaces.nsIDOMWindow);
+        const onWindowLoad = () => {
+            window.removeEventListener("load", onWindowLoad);
+            if (window.document.documentElement.getAttribute("windowtype") == "navigator:browser") {
+                gService._checkWindowFeatures(window);
+            }
+        }
+        window.addEventListener("load", onWindowLoad);
+    }
+}
+
 
 class PolyfillService {
     constructor() {
@@ -624,6 +650,17 @@ class PolyfillService {
         this.isNullishCoalescingSupported = this._checkSyntax("foo??bar");
         this.isNamedCapturingGroupSupported = this._checkSyntax("/(?<Name>x)/");
         this.isPropertyEscapeSupported = this._checkSyntax("/\\p{L}/u");
+        this.isLogicalAssignSupported = this._checkSyntax("let a=3;a||=false;a??=true");
+        // Features that need a Window global to be checked
+        this.isWebComponentsSupported = false;
+        const win = Services.wm.getMostRecentWindow("navigator:browser");
+        if (win) {
+            this._checkWindowFeatures(win);
+        } else {
+            // Addons get loaded before the first Window is created. Instead, delay the check
+            // until the first navigator window is opened.
+            Services.wm.addListener(gWindowOpenListener);
+        }
         this.fixCache = new Map();
         this.rules = new RuleEngine();
         this.exclusion = new RuleEngine();
@@ -633,6 +670,7 @@ class PolyfillService {
 
     destroy() {
         settings.onPrefChanged.remove(this._prefChanged, this);
+        Services.wm.removeListener(gWindowOpenListener);
     }
 
     _loadRules() {
@@ -682,6 +720,15 @@ class PolyfillService {
         return true;
     }
 
+    _checkWindowFeatures(window) {
+        this.isWebComponentsSupported = typeof window.ShadowRoot !== "undefined" &&
+                                        typeof window.Element.prototype.attachShadow !== "undefined" &&
+                                        typeof window.Node.prototype.getRootNode !== "undefined" &&
+                                        typeof window.customElements !== "undefined" &&
+                                        typeof window.customElements.define !== "undefined";
+        Services.wm.removeListener(gWindowOpenListener);
+    }
+
     isSiteEnabled(URI) {
         return this.rules.isSiteEnabled(URI.host);
     }
diff --git a/lib/polyfills.js b/lib/polyfills.js
index 0e35de9..0197a08 100644
--- a/lib/polyfills.js
+++ b/lib/polyfills.js
@@ -310,6 +310,9 @@ exports.Github_enableDiffButton = jss`
       for (let button of document.getElementsByClassName("load-diff-button"))
         button.removeAttribute("disabled");
     }, {once: true});
+`;
+
+exports.Github_disableTurbo = jss`
   // TEMPORARY: hard-disable Turbo navigation to prevent memory leaks in Pale Moon
   document.addEventListener("DOMContentLoaded", () => {
     Turbo.session.elementIsNavigatable = (e) => false;