difference between <br> and <br />

Visually speaking, there's no difference. But if you want valid XHTML, the <br /> is required per spec. I just learned that the night before last myself.

Same applies for other items like <link rel=...>, <hr>, and <img...> tags- they should all be escaped with a />.

I looked for a full list of deprecated tags and couldn't locate the one I was looking for, but I'm sure it's out there...

Does this work with browsers?

Everything works with browsers.... it all depends on how perfect you want your website to be and how accessable you want it to be.

HTML uses <br>.

XHTML is HTML 'translated' into XML format, which requires all tags to be closed. For every <p>, there must be a </p>, etc. Normal XML single tags are of the format <star/> (note no space).

Now most browsers that are used to HTML will choke on <br></br> or <br/>, so some clever person realised that <br /> works. It's valid XML (XHTML), and HTML parsers will accept it.

So for HTML ignore the slash, for XHTML include the slash but make sure you include the space.

Sionvalais, if you are interested, I wrote an XHTML Article recently. You may want to give it a quick look. It will explain everything you need to know about XHTML is a short time. Mirrored here.