diff --git a/src/extension/contentscript-main-override/index.ts b/src/extension/contentscript-main-override/index.ts
index 52f7610..39f648d 100644
--- a/src/extension/contentscript-main-override/index.ts
+++ b/src/extension/contentscript-main-override/index.ts
@@ -1,15 +1,37 @@
-const genericWindow = window as any
-if (genericWindow.aibrow) {
-  genericWindow.ai = genericWindow.aibrow
-} else {
-  if (genericWindow.ai) {
-    genericWindow.ai.__aibrowOverride = true
+/**
+ * This can be safely called multiple times
+ */
+function override () {
+  const genericWindow = window as any
+  if (genericWindow.aibrow) {
+    genericWindow.ai = genericWindow.aibrow
+  } else {
+    if (genericWindow.ai) {
+      genericWindow.ai.__aibrowOverride = true
+    }
   }
-}
-if (genericWindow.aibrowTranslation) {
-  genericWindow.translation = genericWindow.aibrowTranslation
-} else {
-  if (genericWindow.translation) {
-    genericWindow.translation.__aibrowOverride = true
+  if (genericWindow.aibrowTranslation) {
+    genericWindow.translation = genericWindow.aibrowTranslation
+  } else {
+    if (genericWindow.translation) {
+      genericWindow.translation.__aibrowOverride = true
+    }
   }
 }
+
+override()
+
+// <meta http-equiv="origin-trial" headers in the dom may not have been parsed at this point, so we have
+// to wait for document.head to be available and then override otherwise the browser implementation
+// will be injected back over the top.
+//
+// This can be removed when the origin trials have finished, around M136
+if (!document.head) {
+  const observer = new MutationObserver(() => {
+    if (document.head) {
+      observer.disconnect()
+      override()
+    }
+  })
+  observer.observe(document.documentElement, { childList: true })
+}