have just finished a new website using the wonderful "Realtor" YouJoomla template - which aslo included the Multimediabox extension. I actually used the Multimediabox v2.0.
Anyway, after a bit of testing and searching the YouJoomla forums, the minor weird problem I've got is that when displaying the image galleries, on the popup window that displays, the Close button normally displayed at the bottom right corner doesn't show up. However, turn off Joomla core SEF links and the Close button miraculously appears.
I'm also using a third party SEF Component: SEF Advance, but this doesn't appear to be influencing the problem: only when I turn off Joomla SEF in the Global Configuration > Site > SEO Settings does the problem disappear.
The same problem displays on a range of browsers including: IE8, Firefox 3.5.5., Opera 10, Safari, and Google Chrome, so doesn't appear to be browser-dependent.
Here's a link where you can see the problem: Landscape Photo Galleries - Kid Friendly Landscapes - Phoenix, Arizona, AZ - LandscapeCreator.com
I use Firefox mainly: just click a gallery preview image, click a "Next" or "Previous" button and you should see the problem.
Thanks in advance for any suggestions.