When I click on a teleport link in FireFox I get this error message: The address wasn’t understood Firefox doesn’t know how to open this address, because one of the following protocols (secondlife) isn’t associated with any program or is not allowed in this context. You might need to install other software to open this address. I am using the latest version of FireFox (51.0a2 (2016-10-01) (64-bit)) in 64 bit Ubuntu 16.04 In FireFox’s about:config page I have these entries: network.protocol-handler.app.secondlife;/opt/secondlife-install/etc/../secondlife network.protocol-handler.external.secondlife;true The path to the second life application in "network.protocol-handler.app.secondlife;" entry is the same string used in the desktop icon to launch the Second Life viewer, and this icon does successfully launch the viewer. This same path is also proven to launch it in the Terminal Emulator. Why can't my FireFox installation launch the Second Life viewer?