Every time I open an XML file, all I get is blank page instead of tag tree. The file itself is correct and loads okay, I can see it via View Source or in the Firebug. I've tried turning off all my addons, but the problem was not solved. All other browsers (Chrome, Opera) render the same file as an XML tree. I'm guessing that I've messed up my configuration somehow and Firefox now tries to render XML files as HTML ones. I've tried googling, but with no success. Help, please?