NoMoreIE6Please is a widget for WordPress which displays a custom message to update to new browser as specified. You can specify MSIE minimum version 7, meaning, if the user has MSIE 6, a custom message is displayed. Specify Firefox version 13, well, pretty much any Firefox will get this message then.
You can also choose the size of the icons to display, and which browsers you want to show to the MSIE6 user. I.E. disable MSIE and Firefox, then it’ll display only Chrome, Safari and Opera download link.