Not a bug with AppsBrowser as the issue was with the extension seamonkey.tcz.
It is fixed now. What likely happened and how to prevent?
Sometimes we have a local copy of a .info file which is missing the Tags field. Then when we update an extension our local .info file overwrites the ibiblio hosted .info which had a generated Tags field. Hence no more tag field which then breaks AppsBrowser.
Please check when submitting an updated extension that the .info file has a Tags field.