If you are a MATE desktop user using a Liferea 1.10.xx package installed from the official package repositories of your Linux distribution and since the switch from 1.8.xx the trayicon went missing then the reason is very probably that you are using a package build by Ubuntu for the Unity desktop that strips the trayicon support. You can verify wether this is the case in the "Preferences" dialog which should look like this If the trayicon option is not visible than the package doesn't support a trayicon. This is known to be the case for at least Mint17.