Tumblr says i am not registered when i am using firefox but works fine on safari?

i am trying to download a dashbord theme for tumblr and its working for the website but i just cant log in? it says that i have and invalid user name or password so when i asked to send my password to my email it said that i wasnt registered. But when i went to safari it was working fine i just didnt have the dashboard theme. the theme only works in firefox... does anyone know why? i dont want to log out incase my tumblr gets deleted.