The seeds need fruit juice/pulp too to actually ferment. Did you squeeze the tomato into the container so that some juice and pulp were also included? It isn't so much "mold" as froth or scum. ;)

If not, by this time they are likely as done as they will get so I would take them out and dry them now before they sprout. They will most likely germinate fine without further soaking.

For a great discussion on saving seeds from experienced seed savers, check out this post over on the Growing Tomatoes forum too.

Dave

Here is a link that might be useful: Saving Seeds tips

Thank you so much for your advice and the helpful link, Dave! I didn't squeeze the tomato since I was eating it, but I did include all the pulp that I scooped out with the seeds - hopefully that was enough for them to ferment. :) I'll be taking them out and drying them once I get home today.

Thanks again for your help!