I was running ThinLinc 4.14.0 client and got the update dialog for 4.15.0. I clicked 4.15.0, which launched Firefox and opened the download page.
However, the client had completely locked up in the background and I needed to do a SIGKILL to get rid of it. I could see that it had a child xdg-open that was in a zombie state.
Seen on Fedora 38.