Infradoom is a patch release to support broken session logic caused by an express update. Infradoom also has various other nice bits, bug fixes and patches.
From the changelog:
NEW: Broadcast slider is exposed in timeslider so plugins can interact with it
Fix: IE issue where pads wouldn’t load due to missing console from i18n
Fix: console issue in collab client would error on cross domain embeds in IE
Fix: Only Restart Etherpad once plugin is installed
Fix: Only redraw lines that exist after drag and drop
Fix: Pasting into ordered list
Fix: Import browser detection
Fix: 2 Part Locale Specs
Fix: Remove language string from chat element
Fix: Make Saved revision Star fade back out on non Top frames
Other: Remove some cruft legacy JS from old Etherpad
Other: Express 3.1.2 breaks sessions, set Express to 3.1.0