Printing Ledger/Tabloid paper from FireFox 1.5?

When I print from FireFox 1.5, or ThunderBird 1.07 for that matter,
I have the option of using Letter, Legal, Executive, A3, A4, and A5
paper sizes, but not Ledger or Tabloid (11x17). I use this kind of
paper a *lot*, usually for large nspreadsheets or tables, and it
would be good to be able to use it with web-pages.

Is there a way for me to add it in, via the preferences etc.? I
imagine it wouldn't be that hard to for the developers to add it,
just another entry in the list of paper-size parameters, but don't
think I could figure it out from the sources.