Web links in apps do not work

[DaveHighland]

When I click on a web link in any application other than a browser window (Opera), it doesn't work. Usually nothing happens. Sometimes a Konqueror window opens, but the URL bar is blank. Usually I am clicking on a web link in an email (yes, from a trusted source). But this is also the case, for example, when I click on the menu selection Help/Online Help in the Lazarus IDE: nothing happens.

I am using Opera version 56.0.3051.104, Centos 7, Gnome Version 3.22.2.

Additional info: When I click on Applications/System Settings/Default Applications, the dialog that pops up shows Konqueror as the default Web application. However, when I click the drop-down list to change this, Konqueror is the only app on the list. Also, when I select Settings from the Opera main menu, under the heading "Default Broswer" is the message, "Opera is your default browser."

Any suggestions on how to fix this?