Still partially present in Debian Buster 4.19.0-5-amd64 #1 SMP Debian 4.19.37-3 (2019-05-15) x86_64 Gnome 3.30.2, same as @Raul.
Mozilla Firefox 60.7.0

Hi Raul,
Can you please check this out on the latest Firefox Versions and let us know if it is still reproducible?

Sorry, but not used openSUSE or another Linux distro anymore.

I'd like to add that this bug is still reproducible.
My FF info: http://sprunge.us/nG3uLx
My system info: Linux mycroft 5.12.13_1 #1 SMP 1624557694 x86_64 GNU/Linux - Void Linux

Firefox Browser 89.0.1 (64-bit)

I've already tried comment #9 #10 and #15 to no avail.

(In reply to sampaio.mp from comment #25)

I'd like to add that this bug is still reproducible.
My FF info: http://sprunge.us/nG3uLx
My system info: Linux mycroft 5.12.13_1 #1 SMP 1624557694 x86_64 GNU/Linux - Void Linux

Firefox Browser 89.0.1 (64-bit)

I've already tried comment #9 #10 and #15 to no avail.

I should also add that I'm currently on Void Linux, with XFCE 4.16 and Thunar Archive, Firefox was installed by the time I was using Thunar, now I moved to Caja but Firefox will keep opening Thunar. Caja is set as my File Exploret inside XFCE settings.

These are my relevant files:

~/.local/share/applications/mimeapps.list - http://sprunge.us/GZyhn6
/usr/share/applications/mimeinfo.cache - http://sprunge.us/A7pxLX
~/.local/share/applications/defaults.list - http://sprunge.us/1cxZ3A

I even tried editing d-bes services files but to no avail.

In your mimeinfo.cache, your inode/directory is duplicated, and the first entry still contains thunar.desktop reference. You could fix this file, but this would be a temporary fix, because each update-desktop-database call will reset it.

To set a custom long-term priority, you should set a mimeapps.list file, either system-wide in /usr/share/applications, or user-specific in ~/.local/share/applications. defaults.list is a deprecated name for years.
You don’t probably need to add association since the Caja desktop files already contain it; but you have to set this association as the default one. So, instead of:

[Added Associations]
inode/directory=caja.desktop;caja-browser.desktop

you should have:

[Default Applications]
inode/directory=caja-folder-handler.desktop;caja.desktop;caja-browser.desktop;

Finally, I don’t think anymore Firefox should fix these files, because it is not to Firefox to decide which file manager to use by default. This is an upstream issue which should be fixed in desktop environment tools which aim to define default softwares, e.g. XFCE Settings Manager.

Sources:
https://wiki.debian.org/MIME
https://specifications.freedesktop.org/mime-apps-spec/mime-apps-spec-1.0.1.html

Comment #27
Thank you for your attention! Here goes my updated files following your advices.

~/.local/share/applications/mimeapps.list - http://sprunge.us/S2eKRw
~/.local/share/applications/mimeinfo.cache - http://sprunge.us/XQFG5h
~/.config/mimeapps.list - http://sprunge.us/HHO0QK
/usr/share/applications/mimeinfo.cache - http://sprunge.us/LPDX7e

For observation here is my | grep inode output for each file:

cat /usr/share/applications/mimeinfo.cache | grep inode
inode/directory=caja-folder-handler.desktop;lf.desktop;org.xfce.Catfish.desktop;ranger.desktop;

cat /usr/share/applications/mimeinfo.cache | grep inode
inode/directory=caja-folder-handler.desktop;lf.desktop;org.xfce.Catfish.desktop;ranger.desktop;

cat .local/share/applications/mimeinfo.cache | grep inode
inode/directory=caja-browser.desktop;caja-folder-handler.desktop;caja.desktop;

cat .config/mimeapps.list | grep inode
inode/directory=caja-folder-handler.desktop;caja.desktop;caja-browser.desktop
inode/directory=caja-folder-handler.desktop;caja.desktop;caja-browser.desktop
inode/symlink=org.xfce.Parole.desktop;
inode/directory=caja-folder-handler.desktop;caja.desktop;caja-browser.desktop;

Another command that may help
xdg-mime query default inode/directory
caja-folder-handler.desktop

Still, Firefox opens Thunar!

Testing through-out other applications, I can see it is indeed a DE (XFCE) problem, since every other application (besides Steam) opens Thunar when I am on XFCE. I've just tested it with herbstluftwm and while on it Firefox calls Caja without any problems.

Sorry for insisting in this issue.

For me on FreeBSD, Dolphin should be used.

At the time of writing, if neither Thunar nor Dolphin is open, then Show in Folder:

1. opens Thunar; and then
2. opens Dolphin.

If I quit Thunar alone, then using Firefox to show the same file brings Dolphin to the front – without reopening Thunar.

about:preferences#general

• no relevant preference (no match for inode or directory).

% xdg-mime query default inode/directory
org.kde.dolphin.desktop
% grep 'inode' /usr/share/applications/mimeinfo.cache
inode/directory=clifm.desktop;
% date ; uname -v
Sat  3 Sep 2022 13:49:13 BST
FreeBSD 14.0-CURRENT #20 main-n257645-160a2f2cdda8: Mon Aug 29 00:44:34 BST 2022     grahamperrin@mowa219-gjp4-8570p-freebsd:/usr/obj/usr/src/amd64.amd64/sys/GENERIC-NODEBUG
% 

See also: bug 724461, bug 727422, bug 1304650, …

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:mak, could you have a look please?

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