I actually found the settings for it in the top right corner of the page, but figured I'd report it anyway. Basically, the New Tab Tiles have been causing script errors (prompt to stop script) that disable a few navigation controls, like being able to close a tab. Any tab that is open or opened after the script error will not close. I have to restart Firefox for the controls to start working again. I have found that the tiles that have been causing the problems are the one's that Firefox provides, as it still happens when my internet history is clear and not loading any tiles from my history. It doesn't happen every time, but it does happen regularly. I just changed my settings from "enhanced" to "classic" and will see if this helps, otherwise I will just turn it to blank if its still an issue.