Just played with it. I like Chrome better for its more compact title bar (tabs tucked up into the title bar, versus Firefox which puts a page title in the title bar). I was impressed by the "tab pinning" feature then I noticed that Chrome had it as well.

From a security perspective, I'm very impressed by Firefox's CSP (Content Security Policies), which allows a web site to defeat XSS-type attacks in a very simple way. They still don't have Chrome's process separation model, which to me really makes Chrome the superior browser.