This is an update to the post Juniper VPN on Ubuntu 16.04 64-bit. In version 52 of Firefox the support of NPAPI (Netscape Plugin API) was dropper, so most likely your firefox was automatically updated and IcedTea plugin doesn’t work anymore, as well as Juniper.

The solution is to use ESR (Extended Support Release) version of firefox which still has an NPAPI support. You can get it here. After you have it put it under opt folder and create an executable under /usr/local/bin, so that this firefox is used only to create VPN connection:

tar -xvf ./Downloads/firefox-52.0.2.tar.bz2
sudo mv ./Downloads/firefox /opt/
mv /opt/firefox /opr/firefox_for_vpn
sudo echo `/opt/firefox_for_vpn/firefox &` > vpn_firefox

To prevent it from automatic updates go to about:preferences#advanced and choose Never check for updates (not recommended: security risk) option.