I'm still not exactly sure where the problem is.
The "Cancel and resign" option may appear when you log into your account. I assume you can log into your account successfully. If not, please say so.
Can you open the browser console for Firefox before you try to start a bot game? The keyboard shortcut on Windows is Ctrl-Shift-J, maybe its different on Kubuntu. In the menu you find it under "web developer", then "Browser console" (maybe be slightly different, as I'm using a German language Firefox).
This console outputs important information that may give a clue as to why this doesn't work.