Being considered in https://phabricator.kde.org/D18726

While this feature now works when opening firefox on Neon using the desktop file, it doesn't work when firefox loads automatically on a session restore.

How to reproduce:
Open any web page on firefox and check that KDE file dialog is working.
Reboot the computer with session restore enabled
Check the file dialog in the firefox window that opening automatically when the session starts

Actual behaviour:
GTK file dialog appear

Expected bahviour
Native KDE file dialog

Following this doesn't work: https://userbase.kde.org/Browser_Configuration/Firefox_Dialog_Integration

I should also say that the same is true for thunderbird

Not sure we can do much about that. firefox only accepts an internal setting widget.use-xdg-desktop-portal (which would actually be preferable to the env var) when set by the user, so we can't really set it globally. And at the same time the environment injection doesn't work selectively because session restore will call the binary it restores (i.e. the firefox without env vars)

(In reply to Harald Sitter from comment #4)
> Not sure we can do much about that. firefox only accepts an internal setting
> widget.use-xdg-desktop-portal (which would actually be preferable to the env
> var) when set by the user, so we can't really set it globally. And at the
> same time the environment injection doesn't work selectively because session
> restore will call the binary it restores (i.e. the firefox without env vars)

I see, thanks for the answer! At least you know this is happening in case something can be done about it in the future as it makes the feature less useful if it breaks after a reboot.

Just wondering, isn't it possible to specifically block firefox and thunderbird from the plasma session restore, and instead detect if they it was opened on session logout and in which case auto-start them with the env variable?
Just a suggestion