Firefox is a great browser, but i find chrome works best for pretty much everything (in my own opinion of course, i use both of them and enjoy both of them) As for your broadband issue, i'm not exactly sure how metered broadband works (for this reason i'm going to assume it works something like mobile data). On a windows 10 computer, i do believe there is actually an option when you're in settings > Network & Internet > Wi-Fi or settings > Network & Internet > Ethernet click on the name of your connection, and turn on "metered connection" Which should give you more control over your bandwidth usage for that specific connection. Windows 10 as a whole is rather bandwidth heavy and to be quite honest i can't stand it, i'm still mainly using Win7 myself. Just to clarify i don't use Win10 very often so if any of my information is incorrect please forgive me.
Good luck Mouse!
-P