Content shifted to left (FF) and bottom (IE) in Pages only

Yesterday the content section of my site , test.ronsdalepress.com, shifted to the far left of the page (bottom of the page in on pages controlled by page.php only. I’m using my own theme, which is based on the default theme. Pages controlled by index.php and single.php (see test.ronsdalepress.com/blog) continue to display properly. I have no idea what’s going on here. I’ve scoured the code and CSS, I’ve validated, and I’m using Firebug. I’ve even tried rebuilding page.php several times both from my own single.php and from the default theme’s page.php. I’ve also tried renaming single.php to page.php and uploading it. Amazingly, the content STILL shifts to the left when I do this, even though the pages controlled by single.php still work properly. This happens even when I remove all content from the page.

Anyone have any ideas? I feel like I’m going insane trying to figure this out.

Huge thanks in advance for any help. I suspect I may just need a fresh pair of eyes here.