The first apps I need to replace on any new windows machine (after installing FF) are Paint, Notepad, Photo/Image viewer and MediaPlayer. The funny thing is their replacements are all ancient as well, and still awesome because they've been thoughtfully upgraded over the years without destroying their conceptual integrity, or they've just been "done" for decades.
Paint.Net (v3), Notepad++, IrfanViewer, Foobar2000 & VLC