Is there something like:

If(not chrome){add_delay()}

?

So this is part of a larger adblock checker, if the ad doesn’t load within 5 seconds, it fails and triggers the adblocker warning. Since the ad should load in 3, they’ve set it for 5. If you have ubo, you won’t see the warning that it then wants to pop up, it just seems (and is) a 5 second delay. Changing the UA probably removes this from Firefox because then the clientside scripts will attempt to use builtin Chrome functions that wouldn’t need this hacky script to detect the adblock. Since they don’t exist, it just carries on.