I realise that a backslash should never appear in a URL in a form other than a URL escape code, however in this case the URL's are being generated by a .NET application for generating flashbooks. I have contacted the developer of this application with a bug report. In the interim i would like to use .htaccess to rewrite the offending backslashes. This is how the URLs appear in fiddler debugging proxy. www.example.com/folder/folder/thumbs%5C1.jpg I am using Firefox and it looks as though Firefox is translating them into the URL encoded equivalent ( \ == %5C1 ). Interestingly IE translates the backslash into a forward-slash automatically (not adhering to standards but convenient in this case). Is there a way to use .htaccess to rewrite all \ to /?