Configure Site RegEX confussion

[GarnetAnimations]

I keep trying to use the configure site in the context menu but no matter how I try to set it up it does absolutely nothing and I think I've lost my mind at this point.

An example of my most recent attempts were to move tabs from https://www.nexusmods.com/fallout4/mods/ to a different tab, so I right clicked on a mod page and went to configure site, switched to custom, then input
^https?://([0-9A-Za-z-]{1,63}\.)*www\.nexusmods\.com/fallout4/mods/
Which is based on the default /^https?://([0-9A-Za-z-]{1,63}\.)*www\.nexusmods\.com/
And then clicked save, and the tab both did not move and new tabs did not move either. So I then tried using regex101 to debug it & it mentioned that the expression had an error specifically the // part after :. So I changed it till regex101 said it would work
which was ^https?:\/\/([0-9A-Za-z-]{1,63}\.)*www\.nexusmods\.com\/fallout4\/mods\/ and that too did not work. So please tell me I am a moron and that there is a simple fix.

[FurkanKambay]

You need to surround the whole regex with /s. Also, you don't need the second version with the escaped /s. This worked for me:
/^https?://([0-9A-Za-z-]{1,63}\.)*www\.nexusmods\.com/fallout4/mods//