After upgrading from Mac 10.6 to 10.9, firefox creates new windows by an "expanding" animation instead of just appearing. How do I get the old behavior back?

On Mac 10.6.8, when I create a new window by hitting command-N or going to the file menu, or if another page creates a new window, the new window just appears instantaneously. However, after upgrading to Mac 10.9.2, new windows appear by an "expanding" animation, which takes slightly longer than the old "appearing" behavior. (Other apps on my Mac do not exhibit the "expanding" behavior, only firefox.) Was this behavior intentional? How can I get the old behavior back? I am using Firefox 28.0.