Fastboot doesn't run with http://localhost:4200/?fastboot=true, but does on CURL

We have just begun to add fastboot to our project, and have run into this issue.

Starting the server with ```ember serve``` does not seem to use fastboot by default when I visit ```localhost:4200?fastboot=true``` from the browser. It does however run with this command in terminal ```curl 'http://localhost:4200/' -H 'Accept: text/html'```.

The ```ember-cli``` terminal only prints ```App is being served by FastBoot``` when I make the request via CURL, but not if I visit via the browser. Could this have anything to do with our use of a service worker?