It turns out that g_app_info_get_default_for_type is not reached in my system, indeed. When do_GetService() is called in nsGNOMERegistry routines, it doesn't detect giovfs and falls back to gnomevfs. So it is gnome_vfs_mime_* functions that do something wrong, but probably there is no need to bother about these obsolete routines.
The question is - why FF doesn't detect giovfs? I am not a gio expert, maybe something is wrong with system environment/configuration, not with FF? I am using ROSA 2012 Marathon with FF 10.
It turns out that g_app_info_ get_default_ for_type is not reached in my system, indeed. When do_GetService() is called in nsGNOMERegistry routines, it doesn't detect giovfs and falls back to gnomevfs. So it is gnome_vfs_mime_* functions that do something wrong, but probably there is no need to bother about these obsolete routines.
The question is - why FF doesn't detect giovfs? I am not a gio expert, maybe something is wrong with system environment/ configuration, not with FF? I am using ROSA 2012 Marathon with FF 10.