Ok, i've updated this so the only UA sniffing is to discount Safari as it appears to have all the required support but doesn't allow dynamic favicons. I'm quite sure there isn't a way to feature detect this.

Opera now works a treat :)

Indeed it does, thanks!

The library does use feature detection to detect canvas support, browser sniffing is only to fix some small rendering differences between browsers.

Opera 11.61 masking as Firefox correctly shows the favicon notifications, however.