This is a fairly minor problem, but the package README for tumbler is out-of-date. It currently lists the project's URL as http://live.gnome.org/ThumbnailerSpec but GNOME no longer uses the "live" subdomain; requests now get redirected to the wiki. The newer equivalent URL would be https://wiki.gnome.org/DraftSpecs/ThumbnailerSpec ...although this is only a draft specification. I can't find an official page for the actual application :/
Still lists the old live.gnome.org domain in the README.
Updated in git master.