Question: I found out randomly that when browsing an SVN repository from a web browser (f.inst. <http://svn.myserver.com/>) you can append the query parameter `?r=5` to the URL to get files from that revision. So I was wondering: What more can you do from the browser?

It would be great if I could read change-logs or compare revisions right in the browser without the need to install a subversion application.

The SVN server is a Windows server with XAMPP and subversion installed, using WebDAV modules and something like that (I'm no pro)

Thanks for any information, I couldn't find anything about this on Google

Answer: 
From the browser Subverson itself doesn't offer anything else that I am aware of.

WebSVN - <http://www.websvn.info/> - is a popular repository viewer for Subversion. Gives you the functionality you are looking for. Its a PHP app so should be easy for you to install along side the Subversion repository.
All "web browsers" can do HEAD, GET, and POST requests. Some can do OPTIONS, PUT, DELETE, TRACE and CONNECT. To use SVN under XAMPP and WebDAV, you need something that can do PROPFIND requests.

Your WebDAV server responds to HTTP GET requests, using the SVN plugin to get data and directory listings from your SVN repository. If you want to get properties like Size, Date, Comments and everything else, the SVN WebDav plugin expects HTTP PROPFIND requests. 

You can get plugins for some browsers that allow you to type random HTTP requests, or to do WebDav requests, or to do specific SVN webdav or svn: protocol requests. I'm not aware of a 'web browser' that includes native support for HTTP PROPFIND.