Installing EasyTAG causes Firefox to try to use EasyTAG as a file browser
It seems that EasyTAG creates a file association which results in Firefox launching EasyTAG instead of a file browser in certain circumstances.
I am running a recently updated installation of Arch Linux with Firefox 100 and KDE Plasma version 5.24.5.
With EasyTAG not installed, when I go to about:profiles in Firefox and click on any of the Open Directory buttons, the directory in question is opened in Konqueror, which makes sense as that is a file browser.
When I then install EasyTAG, and click an Open Directory button in About Profiles as before, EasyTAG launches. It's a lovely program, but it isn't a file manager. ;-)
After uninstalling EasyTAG, we're back to Konqueror as the handler for the Open Directory button.
So it looks clear that it is EasyTAG which is setting and unsetting this association for Firefox.
In Firefox's Settings, under the Applications subheading, you can "choose how Firefox handles the files you download from the web or the applications you use while browsing", but there's no setting for a file browser there.
This or a very similar problem seems to go way back...e.g. https://forums.opensuse.org/showthread.php/490812-Firefox-tries-to-use-quot-easytag-quot-as-file-browser
It would be good if we could work out how this unwanted setting and interaction between EasyTAG and Firefox is happening.