I am on a site with a support window chat window open that will not close, logging out and in won't help.

I am on the VistaPrint website and have an Ai support window open that I can't close because the entire window is not visible. I need the top of the window available to close it out and unfortunately the window blocks me from doing anything. I have backed out, logged back in and the window is still present. I contacted Vistaprint and they said it was a firefox issue and to try Chrome. I used Chrome and they are correct, I can access everything, went back to firefox and tried but the window is still present, if the window size could be reduced, I could access the top to close it. Please help.