So I was wondering why I was getting the following responses back (404/403) when using Twitter Bootstrap Alpha 4.0 from either MaxCDN or CDNjs in the Microsoft Edge browser.
As long as there is no fix, you can use 3.3.5 which (as opposed to the current 3.3.6) doesn't have that bug.
In testing this myself I could not get it to work in any browser unless I changed it to HTTPS . Using the following code worked in all browsers for me
<link href="http://cdnjs.cloudflare.com/ajax/libs/twitter-bootstrap/4.0.0-alpha/css/bootstrap.min.css" rel="stylesheet" type="text/css" />