Cannot install on Debian 7

Following these instructions: https://help.riseup.net/en/eip/how-to/linux#install-on-wheezy-debian-7 I get to

sudo apt-get install bitmask leap-keyring
Reading package lists... Done
Building dependency tree       
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies:
 bitmask : Depends: soledad-client (>= 0.5.0) but it is not going to be installed
           Depends: leap-mail (>= 0.3.9) but it is not going to be installed
           Depends: python-keyring (>= 0.9.2) but 0.7.1-1+deb7u1 is to be installed
           Depends: python-jsonschema (>= 0.7.0) but 0.2-1 is to be installed
           Recommends: xul-ext-bitmask but it is not installable
E: Unable to correct problems, you have held broken packages.

(from redmine: created on 2014-07-03, closed on 2014-09-09, relates #5872 (closed), relates #6301 (closed), duplicates #6038, duplicates #6070)