User Agent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:96.0) Gecko/20100101 Firefox/96.0

Steps to reproduce:

1. Open a page with option to download image (eg: https://unsplash.com/photos/7xX02q5ktys);
2. Click to download;
3. In the Firefox's popup window, choose the "open with" option;
4. Select GIMP (flatpak) (or any other flatpak app installed that can open images) and wait for the image to open;

Actual results:

Nothing happens.

Expected results:

The image should've been opened in GIMP.

Initially I thought this problem was because of (flatpak-ed) GIMP and I reported a bug: https://github.com/flathub/org.gimp.GIMP/issues/136. Later, I noticed that, despite GIMP's flatpak having access to the /tmp/ folder, the image still wouldn't open there. With the support I received, it was realized that the "open with" option works perfectly only for .deb programs. The problem seems to be with the way Firefox handles flatpak programs.

One detail is, on the second attempt to open the image in Firefox, the GIMP name, that I had selected before, simply becomes "flatpak".

The Bugbug bot thinks this bug should belong to the 'Core::Widget: Gtk' component, and is moving the bug to that component. Please revert this change in case you think the bot is wrong.

This happens because we're using executable got from g_app_info_get_executable (btw should be used for the debugging purposes: https://docs.gtk.org/gio/method.AppInfo.get_executable.html) to launch the application and not g_app_info_launch or g_app_info_get_commandline.

The GAppInfo supports starting up flatpak applications where the simple
command does not work.

https://hg.mozilla.org/mozilla-central/rev/d963218bad26