[orca-list] Avoid December 3 Trunk builds of Firefox

[Marco Zehe <marco zehe googlemail com>]

Hi all!

A bug snug in on Sunday that breaks the complete accessibility hierarchy
on all platforms. So please stay on the December 2 build if you're using
Trunk, and don't let it update you to today's build.

I will let you know when things have been sorted and it's safe to use
Trunk builds again.

Same goes for Thunderbird...

Marco