Question: I'm trying to use Dolphin as file chooser for Firefox in Archlinux instead of Nautilus. I've read [this](https://bbs.archlinux.org/viewtopic.php?id=87574) but it did not solve my problem. The config seems related to firefox as 

```
xdg-mime query default inode/directory
dolphin.desktop

```

Which is right. Also 

```
cat /usr/share/applications/mimeinfo.cache | grep  x-directory/gnome-default-handler
x-directory/gnome-default-handler=kde4-dolphin.desktop;

```

Seems to be right too. What am I missing?

Answer: 
Currently (2018-09-25) there exists no user-configurable way to change this behaviour in Firefox.

This is a known bug: [Firefox does not use default file manager](https://bugzilla.mozilla.org/show_bug.cgi?id=1285711)

It was first reported on Bugzilla on 2016-07-08.
At the time of writing this bug is unassigned and unresolved.
Type `about:config` in the address bar

Search for `ui.allow_platform_file_picker`

Toggle it to **true**

Restart Firefox.