Bug 419869

SUMMARY
If the blocking of outgoing traffic using the rule in iptables is enabled:
sudo iptables -I OUTPUT -m owner --uid-owner your_user_name -j DROP
then when you open the image in the file manager using gwenviev, it does not open, but freezes for 3 minutes or longer.

STEPS TO REPRODUCE
1. run in terminal:
sudo iptables -I OUTPUT -m owner --uid-owner your_user_name -j DROP
2. go to the image directory in the file manager
3. open image with gwenviev

OBSERVED RESULT
Nothing will happen for at least 3 minutes. In the list of processes the process of gwenviev will be visible.

EXPECTED RESULT
Gvenviev should open immediately and show the image

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: this behaves like this on all distributions and shells that I used:
Kubuntu 18.04.2 64-bit
UbuntuStudio 18.04.2 64-bit
UbuntuStudio 19.10 64-bit
Xubuntu 19.10 64-bit
Xubuntu 19.10 64-bit with Plasma
Xubuntu 19.10 64-bit with Mate

ADDITIONAL INFORMATION
If, during the operation of the firewall blocking rule, you start the Gwenviev file manager and not through the shortcut in the application menu, it will open immediately, but when you try to go to the image directory, it will freeze for the same 3 minutes.

This is a very critical bug for me. I use this rule to block traffic and because of this I can not normally use gwenviev as a default image viewer. To use them I have to disconnect the network and delete the blocking rule.