We have a fix for the multiple/non-standard firefox installation issues and should be pushing an update shortly. Until then, the workaround that bartt describes should work.
Looking forward to the fix, since the workaround does not apply.
As I noted, there does not appear to be any files that have been added to ANY of the Firefox installations - nothing is noted in the install log, and the npybrowserplus_2.1.6.dll does not appear to have been placed anywhere on my hard drive.
If simply copying this file in will fix the problem, is there somewhere where I can download this file from?