You hit a basic Windows gotcha. Reinstall FS and it will change back to using FS. Just install over the top of the existing install. Your settings and stuff will remain. Windows uses the last installed program capable of opening a SLURL.  The FS team makes a tool (SLURL-Proxy ) you can use to set which viewer you want SLURL's to use. Save's doing re-installs. You may just want to get it and forget the re-install.