This reverts commit d438a99f4045b35c029656e43011f2c2e9594363.

Doesn't work in firefox: just results in text-encoded <br/>.

When you have <xsl:output method="html">, empty tags <foo/> are emitted
as <foo></foo>. These are equivalent as far as XML is concerned, but
browsers expecting HTML will treat this as <foo><foo>.

I considered just having the output method be XML, but this seems to
cause a number of harder-to-address problems on the browser side.