Ok, got things to work using the workflow below.
The only thing still broken is the Web interface. It doesn't work on Safari. Screenshot with Error Console attached.
admin@router:~$ delete system image
The system currently has the following image(s) installed:
v1.9.0.4901118.160804.1131 (running image) (default boot)
v1.9.1.4939093.161214.0705
You are about to delete image [v1.9.1.4939093.161214.0705]
Are you sure you want to delete ? (Yes/No) [Yes]: yes
Removing old image... Done
admin@router:~$ show system image
The system currently has the following image(s) installed:
v1.9.0.4901118.160804.1131 (running image) (default boot)
admin@router:~$ add system image http://dl.ubnt.com/firmwares/edgemax/v1.9.1/ER-e100.v1.9.1.4939093.tar
Trying to get upgrade file from http://dl.ubnt.com/firmwares/edgemax/v1.9.1/ER-e100.v1.9.1.4939093.tar
% Total % Received % Xferd Average Speed Time Time Time Current
Dload Upload Total Spent Left Speed
100 82.9M 100 82.9M 0 0 9241k 0 0:00:09 0:00:09 --:--:-- 9701k
Download suceeded
Checking upgrade image...Done
Preparing to upgrade...Done
Copying upgrade image...Done
Removing old image...Done
Checking upgrade image...Done
Copying config data...Done
Finishing upgrade...Done
Upgrade completed
admin@router:~$ show system image
The system currently has the following image(s) installed:
v1.9.1.4939093.161214.0705 (default boot)
v1.9.0.4901118.160804.1131 (running image)
A reboot is needed to boot default image
admin@router:~$ reboot
Proceed with reboot? [confirm][y]
