twice when I tried to print to MS XPS Document Writer, Firefox freezes

I installed version 18 yesterday. Now I was trying to print to document writer some information from a website, but it freezes. It gets to show the small dialogbox indicating progress, but then it freezes. I tried to close the dialogbox (cancel button was disabled), and Windows asked me to close the program or wait for the program to respond. It happened twice, with different documents. OS is Windows 7 Home Premium.