SUMMARY *** When editing a backup plan, in the Advanced section, there is an option to set up exclusion filters. A hyperlink is included in the descriptive text to view the backup format. It appears that the the link is trying to open up a hard-coded web browser to view the documentation. The following error is shown in a dialog: "Could not locate firefox executable" In this case, I am using Firefox-ESR, installed from repository. The error is the same if Opera is set as the preferred browser in Default Applications control module. *** STEPS TO REPRODUCE 1. Un-install or disable Firefox by whatever means. 2. Install Firefox-ESR from repository (deb https://ppa.launchpadcontent.net/mozillateam/ppa/ubuntu/ lunar main) 3. Try to access this help documentation OBSERVED RESULT A dialog pops up with the message "Cannot locate firefox executable". EXPECTED RESULT The selected browser from the Default Applications KCM should be called, or the system's default browser as a fallback. SOFTWARE/OS VERSIONS Linux/KDE Plasma: Kubuntu 23.04 KDE Plasma Version: 5.27.4 KDE Frameworks Version: 5.104.0 Qt Version: 5.15.8 ADDITIONAL INFORMATION Other applications (such as kid3, for example) show this type of information in a tool-tip, which would actually be preferable. Loading up a web browser may cause unnecessary delay and other inconvenience. Firefox, for example, can in some situations begin popping up windows from its last session all over the place on every other monitor and virtual desktop. Alternatively, if this documentation being presented is too much for a tool-tip, consider using the KDE Help Centre. Just PLEASE don't call a whole new web browser to reference a filter format! :-/
The link is for a man:// URL, please check system settings for what will open on such a url.
(In reply to Simon Persson from comment #1) > The link is for a man:// URL, please check system settings for what will > open on such a url. I don't know how to check this directly, but I have tried "xdg-open man://tar" and also using KRunner to open "man://tar". Both correctly open Help Centre to the manpages section (although only to the top of the manpages section, not to the tar manpage).
It turns out that the behaviour was caused by a package called "activity-aware-firefox". After purging it from my system, clicking the link in KUP KCM now opens Konqueror to "man:///bup-index". I am still confused as to why a web browser is being called for "man://*" instead of KHelpCentre (which is the handler for man:) but this is not a bug in KUP.