Drupal

Firefox caches form values. Most noticeably, it caches the selected position on select boxes. I less often run into cached checkbox and radio button values... even the occasional cached text box value. If you're a developer, you will be familiar with this and its work-around -- clicking into the url box and hitting enter rather than refreshing while debugging.

I added a brand-new cck field to a content type which already had a bunch of nodes, but previously had no cck fields. This new field needed to have a default value set for all existing nodes. Of course, editing an old node and saving it without making any changes would set an appropriate default value... but I couldn't manually do that for all the nodes.