I am searching for a way to hide url bar or navigation panel. Alternatively I could replace items of navigation panel. How to achieve this?
You can not hide any of the UI elements of Firefox. This was a design decision mainly intended to ensure extensions could not break Firefox. There is some (I think ongoing) discussion around hiding the tab strip, to make sidebar tab extensions nicer.
I think Firefox should use similar idea: [Firefox] Move tabs button to tooltip
I do some work on github: https://github.com/nintyfan/HideMyURLBAR/tree/master