Security/Reviews/Firefox10/SilentUpdateEliminateWait

Items to be reviewed:

Introduce Feature

the chrome approach - having two versions side by side and picking the latest one
- this breaks things that rely on our installation directory being fixed
applying update on shutdown rather than start up - not planned currently

works better
do not want to completely rearchitect how Firefox launches just to get silent updates

not adding lots of new stuff
- changes are to interactions between them
- biggest change is in copying files

Race conditions during copying
- we don't rename anything until we have two fully working versions
Folders/files being locked during rename/copying operations
dealing with issues of crash/fail during update
- update.status is updated to track changes and monitor state
- if a failure state is detected old directory is removed completely and created from scratch
Will Antivirus software freak out because of this relatively unusual behavior?
- likely caught when landed in nightly if there is an issue
  - ZoneAlarm ForceField, TripWire
how do we verify we have a complete and proper copy?
- status file = applying -> update is progressing, if halted in this state then we may have a failure we need to restart
- if anything fails we bail out and write an error code to the file to notify the main firefox instance
- only in success does update.status get changed to success

[QA] If we have a comprehensive plan for "noisy" updates does that cover us for "silent" updates? Are there security "holes" we should be testing for?
- I think a lot of the testing will have to be repeated for the silent case and the noisy case.
- Failure of the silent case that should fall back to the noisy case needs to be tested