I had the same (similar) issue when I installed Webcat in the days when it was better than the Jolla browser. Webcat ‘stole’ the option for opening links from the Jolla browser by default. When I then deleted Webcat, the app had gone but the mime entry (or whatever) was still there to open links in webcat, the result being that links were never opened by anything.
The solution was to edit some configuration file and edit the entry for HTTP/HTTPS to go back to the Jolla browser. Somebody here kindly told me how to do this, but I’m afraid I can’t remember now.
Somebody will know here though!