I had some essential widgets on the left hand side - Quests, The Oracle and Shop List. They've suddenly disappeared in my Firefox browser. I tried removing them and re-adding them but that didn't work. Training Center notifications and shop sales notifications have gone as well. Everything shows up as it should in Chrome.

did you click toggle sidebar up by the clock?

I've just clicked it and got it all back. Thanks for the help. I have no idea how I managed to switch the sidebar off.