You could try the IE Tab or similar add-in for FireFox to get around this (https://addons.mozilla.org/en-US/firefox/addon/ie-tab-2-ff-36/). You'll need to add the various BPOS URLs to the "sites filter" setting but after that you can continue to
use FF as your default browser but the BPOS pages render using IE in the background.
Cheers,
Neil