Is there a firefox extension that can make its default size 800x600?

[BluffTHIS!]

Unless some poker junkie has written one, I don't think there is. I only play 3 tables at at time and usually have my Firefox browser open in the other space as well with lobbies behind it. And you are right that sometimes the minimized size you previously used seems to be forgotten and you have to resize it again. Only takes two seconds though.