Newbie on F-18 can't install T'bird.

A month ago I escaped from M$ to F-16, that I got running reasonably well, FF and T'bird so that I could ask questions. I was not able to upgrade 16 to 18 so I reinstalled and now can't get T'bird installed. The 'Software' add GUI hangs at "Waiting in queue."

Help suggestions, please, gently, I am GUI-centric.

Happy Easter, happy Spring!