So I seem to have fixed the issue by replacing the Poser.ini file with a backed up file. FF renders smoothly now.

The difference between the old ini file and the new ini file, besides the expected recent files and UI details, was a line saying 'MAT_WACROS_ON' and in the old file it was set to 0 whereas in the new one its set to 1. How did that ever get set to 0 I wonder? Is there a checkbox hidden somewhere?

"The fool is not the one that does something foolish, but the one that does nothing at all."