GIMP depends on gvfs, but it is not listed in INSTALL.in
Simple issue, I originally discovered and reported it downstream: https://bugs.archlinux.org/task/62124
If you use File -> Open Location to try to download a file from the web, it works if you have gvfs installed and hangs if you don't. Either gvfs should be added as an official GIMP dependency, or else the downloading method should be reworked to not depend on gvfs or fail with a reasonable error message (if the dependency on gvfs is meant to be optional).