Find the URL for the file and then replace the changeset identifier with tip.

How do I change the style of the web interface to the visually more attractive gitweb?

In [http://www.selenic.com/mercurial/hgrc.5.html hgrc] set 

[web]
style = gitweb

To switch back to the default style specify "style = default" (see [http://hgbook.red-bean.com/hgbookch6.html#x10-1390006.6.5 hgbook]).