From MozillaZine Knowledge Base
This preference turns on app.update.mode and allows automatic download and install to take place.
Possible values and their effects
ask the user what he wants to do when an update is available
download and install updates automatically, possibly with a warning if incompatible extensions are installed (see app.update.mode)
- app.update.enabled must be set to true for this preference to take effect.
First checked in
Has an effect in