This problem cropped up shortly after the move to firefox v48.x and has been getting worse... this is no isolated to one machine but dozens... The call ins have been growing steadily and I've personally been running into it quite often. There doesn't seem to be any rhyme or reason... anything online suggests an extension/add-on but that's the funny thing, Almost all of these issues are happening with a clean add-on free (outside of those firefox includes) with ZERO 3rd party background apps. Basically right now all I have to do is load up firefox.... and if I open a new tab... suddenly firefox is downloading garbage data as fast as anyone's internet is capable of which results in any pages trying to be loaded failing with a connection error. You can latterly set each tab or close all but one tab and go to google... or stop it from loading anything (go to a blank page) and check the task manager and it'll be PEGGED until you close the browser RIGHT down... sadly the moment you fire it up again.. it'll go nuts. NO it's not downloading an update or a newer version of firefox.. Did a recent full windows clean install.. downloaded and installed firefox freshly.... loaded it up... went to the typical driver locations with each location having it's own tab.... after the 3rd tab was opened, nothing worked... bandwidth capped. I can't seem to find ANYONE else having this distinct issue and every time I try and view the firefox forums they are under maintenance.