I discovered an interesting bug in Firefox today. While working up a layout for a new design, I created a directory with the design version number in it, "1.5". Upon viewing the page in Firefox, I discovered that the relatively linked stylesheet was not being applied. Amazingly it worked as expected in IE. (Well, except for the box model, and the margin:auto, etc.) I half-heartedly searched google and del.icio.us for similar issues. I reinstalled firefox and disabled some extensions. I did a virus scan (some other programs had been acting up). No dice.
And then I did what I should have done in the first place: I blamed myself, not the program -- and replaced the period with an underscore. Everything works fine now. Except IE, needless to say.