Hi,

Is it possible to have a Firefox-LiberKey built that contains some useful Addons/Extensions like TabMix, Xmarks, Session Manager etc.

Perhaps it will be a good idea to have the Firefox-LiberKey built with its own personalized version of LiberKey inspired theme

Other than that, I absolutely love LiberKey.

You can use Add-Ons and personalize your Firefox in your LiberKey, there is no problem with that. The Add-Ons and your personalizations (e.g. Background image...) will remaint after an update of Firefox.

Please notice that some (really few) addons may be not portable and their settings could be lost on another computer.
But to be honest, I encounter only one of them (profileswither)

I use Mozbackup to copy all my addons from my PC to my Liberkey. So I have the same configuration on both. After that, I shut down the addons that I don' realy need on the Key.