The original thread provides more context. And acc. to a commenter there it’s part of some anti-ad blocker code - it builds an HTML fragment that should take 3s, then waits 5s, then checks if the fragment is gone. Another user mentions that “[it tries to detect FF only, not Chrome] Probably because there are other methods for Chrome that don’t apply to Firefox.”
The original thread provides more context. And acc. to a commenter there it’s part of some anti-ad blocker code - it builds an HTML fragment that should take 3s, then waits 5s, then checks if the fragment is gone. Another user mentions that “[it tries to detect FF only, not Chrome] Probably because there are other methods for Chrome that don’t apply to Firefox.”