I initially raised a support request here: https://support.atlassian.com/browse/CSP-51135 where I was told that even though the Firefox Plugin that Benryan initially developed was now the property of Atlassian, because it still contains the following license in the source I cannot modify it internally to work better in our environment.
We have Confluence tightly integrated with our portal and would prefer to remove the extraneous warning message when open docs from our Confluence instance. Do do this will require modifying the source of the plugin.

// Copyright 2008 Benryan Software Inc.
// All rights reserved.
// THIS IS NOT OPEN SOURCE SOFTWARE
// Unless you are a Word/DAV licensee, Benryan Software explicitly denies you the right to copy, modify,
// create derivative works, or re-distribute this software. Only licensees of
// Word/DAV for Confluence can distribute this software for use with Word/DAV for Confluence.

Available from: https://update.atlassian.com/office-connector/URLLauncher/1.0.4/webdavloader.xpi

What I'm after is this text being removed from all the files included in the Firefox plugin. Replace it with the standard Confluence licensing?