Sometimes while using Top Sites the panel will refuse to load any content and show the default state with default top sites and no highlights. This might be related to the metadata table causing the query to fail. Both Bryan Bell and I experienced this issue. I haven't been able to reproduce this issue reliably, But it happened to me after tapping on a highlight or topsite and going back to the TopSites home panel. Also simply reloading the panel by opening a new tab or switching back to a panel doesnt load anything. Going to the history panel shows visited sites but the topsites is still empty.