Question: I installed Ubuntu GNOME 16.04.2, setting the system language to German during the installation. However, the Firefox user interface uses English. The package `firefox-locale-de` is installed. I even set `general.useragent.locale` under `about:config` to `de-DE`, `de_DE`, and `de`, but none of these helped. How can this problem be fixed?

Answer: 
I had a similar problem while updating from 16.10 to 17.04. The problem was solved by adding the following lines to `/etc/NetworkManager/NetworkManager.conf` and then restarting the computer.

```
[device]    
wifi.scan-rand-mac-address=0

```
I was facing similar issue after upgrading from 16.10 to 17.04.
It is likely that this is happening because your device's MAC address is being randomised automatically. You can verify that by checking your MAC address using the `ifconfig` command (if you remembered the original address).

How to fix:

Add the following line to `/etc/NetworkManager/NetworkManager.conf`:

```
[device]
...
wifi.scan-rand-mac-address=0

```

Now save the file and restart network manager using:

```
sudo systemctl restart network-manager

```

Now reboot.