It always takes me logging in twice to get into the Gallery when using firefox. I log in .... click the link at the top to go to the Gallery ... it doesn't show that I logged in ... then I click the link to Forums at the top and it takes me back to that page ... I log back in again ... then click the Gallery link again ... and it lets me in every time.
With Firefox .... sometimes you have to nudge the hamster wheel a bit.