This might be a know issue, but testing this PR locally I found that the removal of these lines caused the background of all pages to be completely black. The only thing that's visible in a document is the images. Adding these lines back seems to fix the issue.

My configuration: Windows 7 (64-bit), Nightly 22 (Mozilla/5.0 (Windows NT 6.1; WOW64; rv:22.0) Gecko/20130313 Firefox/22.0 ID:20130313031041 CSet: c1a5c44ae3d8), HWA on with DirectWrite 6.2.9200.16492.