Tumblr supports Chrome a lot better than it supports Firefox. When they introduce a new feature, or change something, it usually works in Chrome from the beginning, but may take quite some time till it works in Firefox. Such was the case, for example, with the new editor introduced earlier this year.
Now there’s something especially weird. The Esquire theme (I use it for Vivat Crescat Floreat, Thirteen to Fifty, and The Latin World) shows an ugly anthracite bar at the top of the page—in Firefox, but not in Chrome.
The ISA-Bus 