I found it impossible to debug very large scripts on Firefox. Searching for a string in the script is next to impossible, it would hang the interface for minutes. In Chrome it take seconds to do something similar, you can tell that the script is too big but at least it's debuggable.

Also as a user I cannot bear to use Firefox. I recently retried it (can't recall the version, IIRC it's the first version they introduced multiprocessing) and it still underperforms: I experienced (sub second) lag on UI interactions whereas I wouldn't using Chrome.

never had slow search on Firefox. also Firefox can search a string on all source files, while chrome you have to know the file beforehand