I got what looked like a normal Waterfox update so ran it, and links in emails now don't work - "Application not found". Waterfox (49.0.2) is still listed as installed but the shortcut (on the menu bar) has disappeared, and "uninstall" gives "an error occurred and it may already have been uninstalled". I could reinstall but would that help with the link application? 40 mins later. Crisis over. Reinstalled Waterfox and all seems well.