Gvfs-open error opening location: The specified location is not supported

I’m running Unreal Engine 4.14, compiled from origin/4.14 (ab5adcb27), on Debian 3.16.36-1+deb8u2 (2016-10-19) x86_64 GNU/Linux. When trying to open a project that uses the substance plugin, it asks if I wish to download that from the marketplace, but that fails with the following message, and then exits the editor:

gvfs-open:
com.epicgames.launcher://ue/marketplace/content/2f6439c2f9584f49809d9b13b16c2ba4:
error opening location: The specified
location is not supported

Exiting abnormally (error code: 1)