ClickToFlash is a WebKit plugin that prevents automatic loading of Adobe Flash content. If you want to see the content, you can opt in by clicking on it or adding an entire site to the whitelist.
Try control-clicking (or right-clicking) on an unloaded Flash box to access ClickToFlash's contextual menu which allows you to do advanced things like edit its whitelist, specify settings, and load all Flash on the page.
Version 1.6b9: Release notes were unavailable when this listing was updated.
- Mac OS X 10.4 or later