Alas, but the lake of the good and evil still doesn't work in Firefox. Have you considered possibility that it has something to do with graphics? Like maybe Chromium is able to use hardware acceleration, while for some reasons Firefox uses software rendering here and here. Probably something graphically fancy happens on said level, something that was NOT used on the first and the second level.
Can you describe the problem in more detail?
I am testing in firefox. I took the first mission for the magicians, passed it, then I went to the guild window and getreward button was on, I click and everything is ok.
As I understand, when you complete mission and go to guild window getreward button is not active , yes?