Cleanup iceweasel prefs
We have a bunch of probably obsolete prefs, and some others that are apparently not respected. See blueprint.
Blueprint: https://tails.boum.org/blueprint/cleanup_iceweasel_prefs
Feature Branch: feature/ff24
Related issues
- Related to #6370 (closed)
- Blocks #5706 (closed)
Original created by @tails on 5768 (Redmine)