In Firefox, you will get a box that looks like this when you click on the Subscribe to: Posts (Atom)  link:

To learn more about RSS feeds in general, see this info copied from the Internet Explorer Help page explanation of web feeds (RSS) here:

Using web feeds (RSS)

Here are answers to some common questions about using feeds (RSS) in Internet Explorer (from the IE Help Pages)

What is a feed?

A feed, also known as RSS feed, XML feed, syndicated content, or web feed, is frequently updated content published by a website. It is usually used for news and blog websites, but can also be used for distributing other types of digital content, including pictures, audio or video. Feeds can also be used to deliver audio content (usually in MP3 format) which you can listen to on your computer or MP3 player. This is referred to as podcasting.

How do I know if a website offers feeds?

When you first view a website, Internet Explorer will search for feeds. If feeds are available, the Feeds button will change color and a sound will play.

How do I view a feed?

When you visit a webpage, the Feeds button will change color, letting you know that feeds are available. Click the Feeds button, and then click the feed you want to see. To get content automatically, you should subscribe to a feed. Click Related Topics to learn how to subscribe to a web feed.

How does a feed differ from a website?

A feed can have the same content as a webpage, but it's often formatted differently. When you subscribe, Internet Explorer automatically checks the website and downloads new content so you can see what is new since you last visited the feed.

How can I automatically get updated content?

You can receive content automatically by subscribing to a web feed. When you subscribe to a web feed, you set the interval at which Internet Explorer will check the website for updates. Once you've set an interval, Internet Explorer will automatically download the most up-to-date web feed list. Click Related Topics to learn how to subscribe to a web feed.

Does a feed subscription cost money?

No, it's usually free to subscribe to a feed.

How can I view my subscribed feeds?

You view feeds on the Feeds tab in the Favorites Center. To view your feeds, click the Favorites Center button , and then click Feeds.

Can other programs display my subscribed feeds?

Yes, Internet Explorer provides the Common Feed List to other programs. This allows you to subscribe to feeds with Internet Explorer and read them in other programs, such as e-mail clients.

What does RSS mean?

RSS stands for Really Simple Syndication, and is used to describe the technology used in creating feeds.

What formats do feeds come in?

The most common formats are RSS and Atom. Feed formats are constantly being updated with new versions. Internet Explorer supports RSS 0.91, 1.0, and 2.0, and ATOM .3, 1.0. All web feed formats are based on XML (Extensible Markup Language), a text-based computer language used to describe and distribute structured data and documents.