How do I browse an old revision of a Subversion repository through the web view?

Append something like this to your repository URL:

!svn/bc/<revision_number>/

E.g.

http://www.example.com/svnrepository/!svn/bc/3/

Alternative

From Bert Huijben’s comment:

If your repository is hosted using Subversion 1.6.0 or later, you can
use example.com/svnrepository/?p=3 for the same result… This method
/is/ documented. (?r= revision of the file, ?p= operational revision
of the URL). See the subversion 1.6 release notes