re-captcha plugin problem – wrong display on Firefox

I have a problem with display properly captcha form on FF5

for example: http://bicyclegirls.pl/?p=86 screenshot: http://i55.tinypic.com/otgpiv.jpg

IE and Opera works perfect: http://i52.tinypic.com/iolq2x.jpg

I’m using WordPress 3.1.3 with Unstandard 2.01 theme, any idea, how to
fix it?