Are you setting the paper size preference to 4x6 size paper thru Firefox?

You need to initiate printing - {Ctrl + P}, then check to make sure your printer is selected in the Printer - Name dialog window, then hit the Properties button. Go to the tab for Paper Size and select the 4x6 size, if your printer software offers that size to choose from. That setting with be held in Firefox until you select a different paper size.

thanks for the response Yes I've done all that and it still wont work, infact the printer doesn't offer that size but I can add it as a custom size, and I've tried that.