An internal site with that code running there is probably going to be tested if any browser updates will be performed. Upgrading to Firefox will mean that you

An internal site with that code running there is probably going to be tested if any browser updates will be performed. Upgrading to Firefox will mean that you will effectively have to perform these checks twice. (No, you are not going to get everyone to use Firefox, it is a different browser, hence "scary" for most users.)