https://tech.slashdot.org/story/17/02/04/2323204/mozilla-to-drop-support-for-all-npapi-plugins-in-firefox-52-except-flash

What does this mean to Documentum? Well, if your Webtop/D2 is using applets (UCF), starting March, you’ll only be able to use it with IE11 and older versions, as no other major browser (actually, Firefox is the only “major” browser that still allows NPAPI plugins, but this is due to their slow pace of development) will allow NPAPI plugins (Java).