Comment 14 for bug 1551171

Using gio is a desktop independent way of doing that and isn't tied to GNOME. It's a hard dependency of gtk anyway. It implements everything we want, but it actually works (whereas xdg-mime and friends are pretty much unmaintained and are known for not being very reliable)

I'm still not sure what's causing your current problem though. This has worked fine in the past with gnomevfs