Thanks for the report, Ray and subsequent commenters. I'm pretty sure the issue is not with Firefox. If what you observe is occurring in longer threads, most likely the issue is with the threads being long, for aforementioned reasons.
We have enabled a weekly update that brings thread counters back into sync with reality. However, because it is only weekly, long threads may see a few days of strange page counts.
Again, the easiest way to deal with long thread misbehaviors is simply to start a mk. 2 version with links between the old and new threads. Thanks!