It's difficult to write complex HTML pages that display well at all screen/text sizes. Most pages are optimised for 800x600 or 1024x768
When I got new monitors and changed to 1280 x 1024 (x2) I found I had to increase the size of the type on some websites in order to read 'em comfortably and that played havoc with the layout, as you describe.
Eventually after some tinkering with the OS font display sizes and Firefox settings I have managed to get to a reasonable compromise.