Problem with backuping - extension is unable to load cfiles

[kogut]

Environment

Steps to reproduce on Firefox 44.0 on Lubuntu 14.04:

How to reproduce

Go to AdBlock preferences (ctrl+shift+f)
Select "Backup and restore" dropdown at lower left
Select "create new backup"
select location (in my case "desktop/tmp")
type "test" in filename field
use "restore own backup" in the same dropdown menu
navigate to the selected location (in my case "desktop/tmp")
backup file is invisible
After renaming file to end in .ini (fix for issue found thanks to ​https://github.com/adblockplus/adblockplus/search?utf8=%E2%9C%93&q=backup.complete.title )

Observed behaviour

It is impossible to load backup without reading source.

Expected behaviour

AdBlock creates file with correct extension or it is not limiting loadable files by extension.