I just finished looking at the code implementing Mozilla's RSS support (aka 'Live Bookmarks') and came up with these tips:

To make the orange RSS button show up on the bottom right corner of Firefox when your webpage is displayed, add following HTML fragment to your webpage's HEAD element for each feed.

<LINK type="{feedMimeType}" rel="alternate"
    title="{feedTitle}" href="{feedUrl}">

where {feedMimeType} can be:

application/rss+xml
application/atom+xml
application/x.atom+xml

if {feedMimeType} is not one of the above then {feedTitle} has to be one of the following (case-sensitive):

rss
RSS
Atom

Otherwise, {feedTitle} can be anything.

To make feed items appear correctly in Firefox bookmark sidebar, your feed items *must* have both non-empty 'title' and 'link' tags.

And what do I think of Firefox's so called RSS support?  Words like crappy and useless comes to mind.

Update #1:

Following is a copy of my comment to Dan Gillmor's post quoting my 'crappy and useless' comment:

Some details behind my rather rude comment:

1. There is no such thing as RSS support in Firefox 1.0PR. Firefox 1.0PR *uses* RSS feeds to implement Live Bookmarks. While Live Bookmarks is useful for del.icio.us, live bookmarks are read-only.

2. While such use of RSS is laudable, they failed to distinguish between Live Bookmarks, a specific application of RSS, and the RSS technology, creating confusion as a result.

3. Live bookmark behavior is inconsistent across feeds. For link blogs, live bookmarks point to different destination sites. For other blogs, they point to different sections of a page or different pages at the same site. Live bookmarks confuses and wastes bandwidth.

4. Bookmark sidebars are too narrow to display item titles effectively.