Different browsers may print on different numbers of pages

One of my programs generates paper forms as HTML documents and brings up a browser for the user to print them. I had made sure the form would fit on one page, but one user was getting it printed on two. Upon investigating, I found that user's default browser was a moderately old version of Internet Explorer, which I had not tested on. Apparently not all browsers will size elements or the margin the same when printing, so even extremely simple arrangements should be tested on many browsers.