diff --git a/lib/main.js b/lib/main.js
index 64f41f3..0cf169d 100644
--- a/lib/main.js
+++ b/lib/main.js
@@ -146,8 +146,10 @@ function supersededFixes(service) {
     // If possible, decied based on the UXP platform, not the application or version
     // Keep entries in each block in the same order as in evaluateFix's switch statement
     const superseded = new Set();
-    if (service.isPlatform51Up) {
+    if (service.hasqueueMicrotask) {
         superseded.add("std-queueMicrotask");
+    }
+    if (service.hasOptionalChainingOperator) {
         superseded.add("dhl-optchain");
         superseded.add("tmx-optchain");
     }
@@ -550,7 +552,16 @@ class PolyfillService {
     constructor() {
         this.isSeaMonkey = Services.appinfo.name == "SeaMonkey";
         this.isPaleMoon = Services.appinfo.name == "Pale Moon";
-        this.isPlatform51Up =  Services.vc.compare(Services.appinfo.platformVersion, "4.8.5") >= 0;
+
+        // Detect available platform features
+        // - queueMicrotask
+        this.hasqueueMicrotask = typeof queueMicrotask === "function";
+        // - Optional Chaining Operator (?.)
+        var code = "this?.fourtytwo";
+        var valid = true;
+        try { new Function(code); } catch(exc) { valid = false; }
+        this.hasOptionalChainingOperator = valid;
+
         this.fixCache = new Map();
         this.rules = new RuleEngine();
         this.exclusion = new RuleEngine();