I stumbled across this problem whilst editing some pages at work; I was using Notepad++ to edit some html and css files (that came from a Visual Studio project) and when i was previewing the build in Firefox, i noticed a gap at the top of the page – on closer inspection i found that they were caused by three ASCII characters (¡<¿)

Asking one of the developers we found that removing the following metatag from the code (meta http-equiv=Content-Type content=text/html;  charset=ISO-8859-1) also removed the problem… After a bit of digging we replaced the metatag and found that swapping the document encoding between UTF-8 to ANSI could essentially turn on and off the problem… The developer in question suggested that Visual SourceSafe (where the file came from) may have corrupted the document at a binary level, so a replication of the file eliminated the problem…

Ze plot thickens….