I installed the version before the 4 July 2011 weekend (6.x-1.0-rc6) and the button appeared OK in Firefox 4 on the Mac. I did not test on Safari 5 or Chrome 12, thinking it would be OK.
When I prepared to install on production today (6 July 2011), I was surprised to find a newer version (6.x-1.0-rc7) with a different config screen. However, I find that, like the previous version, it is not rendering in Chrome or Safari. I also cannot find it in the HTML source for either browser in the way I can on Firefox with Firebug.
The client likes adding this and how it appears on FF4/Mac. However, if it can't be rendered on Safari or Chrome then it won't be useful for us. Have just received a report that it is not working in IE/Win either.