To help protect Firefox users from malicious add-ons, Mozilla will soon require that all add-ons are "signed" (this mathematically proves that Mozilla has verified that the add-on is safe).
As part of this process, you will see a new KeeFox update released soon (due on 28th May). I'm not sure whether this will be given a new version number or if it will just be a refreshed version of 1.4.7.
You won't benefit from performing the usual browser restart after the add-on is installed - it won't do any harm but can just as easily wait until you next need to restart your browser for another reason.
Note that Mozilla will only sign the most recent version of an add-on so if you have not yet upgraded to version 1.4.7, please do so soon.
The situation for beta releases of KeeFox is unclear but it is unlikely that you will need to take any action. If you don't see an update to the beta version at the end of May don't worry (it won't be that much longer until a beta of KeeFox 1.5 will be released anyway).
Mozilla are rushing this process so there is a small chance that the situation will change but I won't mention changes on this site unless they are significant. To keep track of Mozilla's latest plan and read more about the reasoning behind this change, see this Mozilla wiki page: https://wiki.mozilla.org/Addons/Extension_Signing