Turns out ScribeFire and Disqus don't play so well together.
When using the ScribeFire add-on for Firefox to post to a Blogger blog, Disqus commenting gets disabled, and Blogger commenting gets re-enabled. After using ScribeFire, I find it is necessary to then edit the post, show post options in the lower left and disable commenting, with the hide existing option. This then re-enabled Disuqs commenting. Note, disallowing comments but showing previous does NOT re-enable Disqus.