Ok. I have been noticing this speck on the top left corner of the Gmail window from quite sometime now but I am at a loss of words to describe what exactly the “graphic” is supposed to be. It started appearing or rather I’d say I started noticing this graphic some 15 days back but never bothered to find out what exactly it was. It looks something like: ( image courtesy TechCrunchIT)
That was reason enough for me to google it out and I found out I was not the only one who had noticed this.
www.techcrunchit.com/2008/07/05/the-mysterious-grey-box-on-gmail
This link here has an explanation and readers have also have some real “wacky” opinions on what the graphic is. Strange as it seems it appears only in Firefox and Safari browsers not in IE.
And as mysteriously the “box” started showing up it disappeared just as mysteriously. 
