Text disappears in Firefox/Thunderbird

[Alex Hanson <alex%alexhanson.org@localhost>]

I am using NetBSD 4.0, but this problem has been present for me a long 
time--across several upgrades and reinstalls of NetBSD. Here is my 
current setup:

OS: NetBSD/amd64 4.0
Firefox: version 2.0.0.13 (compiled with pkgsrc)
Thunderbird: version 2.0.0.12 (compiled with pkgsrc)
Xorg: Currently using modular, have used the single package in the past, 
always compiled with pkgsrc

When I use Firefox or Thunderbird and there is any "letter-spacing" CSS 
setting (e.g., "letter-spacing: 1px") much of the text disappears. The 
first word or two on a given line appears, but after that, I have to 
highlight the empty with the mouse to read the text (Ctrl+A doesn't fix it).

Here's a page where virtually all of the content does not appear 
("letter-spacing: -1px", but the problem persists with any non-zero value):

http://www.thecodecave.com/article337

And relevant screenshots:

http://img68.imageshack.us/img68/9992/invisibletextgs9.png
http://img382.imageshack.us/img382/1842/visibletextlg4.png

As you can see, I compile all of my packages from source with pkgsrc. I 
do not know how binary packages behave in comparison.

Thanks for any help.

-Alex Hanson