diff --git a/gatsby/onPreBootstrap.ts b/gatsby/onPreBootstrap.ts
index e1fbcb23c993..eefbc65fa2b8 100644
--- a/gatsby/onPreBootstrap.ts
+++ b/gatsby/onPreBootstrap.ts
@@ -114,6 +114,24 @@ posthog.init("${process.env.GATSBY_POSTHOG_API_KEY}", {
         if (!hasInAppFrame) {
             return null
         }
+        // Browser extensions (e.g. Dark Reader) inject an inline script. When it
+        // throws, its single frame is "global code" at line 1 of the document URL
+        // and is marked in_app, so it reads as a first-party error and each new
+        // page URL mints a new fingerprint. Our own code loads from separate script
+        // files, never inline in the page, so this shape is always extension noise.
+        var documentUrl = window.location.href.split('#')[0].replace(/\\/$/, '')
+        var isInjectedInlineScript = exceptions.some(function (ex) {
+            var frames = (ex && ex.stacktrace && ex.stacktrace.frames) || []
+            if (frames.length !== 1) {
+                return false
+            }
+            var frame = frames[0]
+            var filename = (frame && frame.filename ? frame.filename : '').split('#')[0].replace(/\\/$/, '')
+            return frame && frame.function === 'global code' && frame.lineno === 1 && filename === documentUrl
+        })
+        if (isInjectedInlineScript) {
+            return null
+        }
         return event
     },
     person_profiles: 'identified_only',