Evie, that would be because your likely using 800 x 600 resolution, being an older resolution. Your buttons at the top are likely fallen too two rows. The design is built for higher resolutions, being not many use 800 x 600 resolution anymore.
Veiled, IE7 changed because of firefox, being firefox had developed all these new features that IE have now copied into their IE7. So yes, firefox have just gone further. What you don't see with firefox, is that firefox allows you to add things into the browsers functionality, being "add-ons", thousands of little scripts which make using the browser more functional depending on whay you do upon the internet. You can find those scripts and links at the firefox site. Thousands of develpers around the world write add-ons for firefox increasing its performance, little tidbits basically, that people want to do, so they write an add-on script to do it, then make it public.
For example, back in the first post I wrote about one I use, which replaces the google toolbar that many may have installed, and instead places things like pagerank, alexa ranks, etc, down in the bottom right of the browser, thus not taking up any actual readable screen space and instead incorporating aspects into the already present brower frame, using browser real estate as such more effectively if you like, so you don't have toolbars taking up your reading space.