Must be differences between your copy and mine that aren't reflected in the version number. Say, do certain threads (example thread here) not load completely for you? My copy of NS 4.77 stops loading after #55 with any CSS I have loaded, though it does load the entire thread without any CSS.
First, the rest of the posts are indented, even the to and by lines.
Second, the special formatting of the to and by lines is gone (i.e. bold, underline, etc.)
Third, the font goes into a light, thin like version of the current font.
Funny thing is, I can't find any open tags between your post #55 and the following post where the "weirdness" starts.
The other interesting note, my CSS almost works in IE 5.5. The only difference is the left and right borders appear. Font styles are there though, so it must have something to do with NS and open zero pt borders. Maybe?
It seems so. I quickly just changed my CSS to include both the left and right border width set to zero and IE handled it beautifully. MS did something right? ;)