[Tails-dev] [patch, please review] generate Iceweasel prof…

Hi,
attached patch should generate Iceweasel profile on build time, rather than
run time. It is required for a "bookmarks" persistence preset (which I want
to implement soon), as explained in the todo ticket:

https://tails.boum.org/todo/persistence_preset_-_bookmarks/

First time I send a patch, I hope it's ok :-)

Alessandro