Help, please! Setup MM2 behind firewall / proxy

[Wominator]

Hi!
I read and tried a lot, without success. I’m not able to get MM2 on Pi3 running in our company. It always runs against the firewall. I just need to configure the right proxy http://proxy.xxxxx.de:8080 for Electron. Systemwide proxy-config in /etc/environment etc. isn’t recognized.
Any ideas / links, where I can get help?

Thanks in advance
Womi