The implementation of Frames in the specs are a bit troublesome. Basicly all browsers today breaks the spec, becuse the way it's implemented requires code that would severly slow down the display of webpages and to make matters worse, in complex situations it's not even really clear how things should work.
These problems to a large part is probably due to that frames where partly ignored since the W3C at the time thought that they had several bad traits and should be phased out entirely (that is why frames in HTML 4.01 and XHTML 1.0 tags and attributes only exsists in the Frames and Transitinal DTD, and XHTML 1.1 doesn't have the at all).
Anyway there is a very old and long bugreport over at Mozilla detailing the problems involved if you are interested http://bugzilla.mozilla.org/show_bug.cgi?id=3655 , but for most uses it's enough to know that there is a resonably harmless hack that works in basicly all browsers in use today removing borders between the frames, while still only using 1 invalid attribute .
When I use framesets I use something like this (or the corresponding HTML). This will work in next to all browsers (IE, Mozilla-family as well as Opera, which is 98%+ of the browsers in use).
<?xml version="1.0" encoding="iso-8859-1"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Frameset//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-frameset.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
<meta name="author" content="Stefan Huszics" />
<meta name="copyright" content="Stefan Huszics" />
<meta name="publisher" content="Stefan Huszics" />
<link rel="SHORTCUT ICON" href="img/page.ico" />
<frameset cols="100, 1*" border="0"> <!-- border="0" is a bugfix for IE, NS as well as Opera -->
<frame name="nav" src="nav.html" frameborder="0" marginwidth="1" marginheight="1" scrolling="auto" />
<frame name="main" src="home.html" frameborder="0" marginwidth="1" marginheight="1" scrolling="auto" />
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For the future you might be interested in knowing that farmes will make a comback in XHTML 2.0 as X-frames, which is a modernized version that solve some of the largest culpits that was the reason frames where dropped from the specs to begin with.