Remove / from www.example.com/ [closed]

This isn’t a WordPress thing, this is a browser/HTTP thing. Firefox may be showing the / as part of a setting, but example.com and example.com/ are the same URL.

This Q on webmasters goes into more detail as to why this is the case:

https://webmasters.stackexchange.com/questions/35643/is-trailing-slash-automagically-added-on-click-of-home-page-url-in-browser