Userscripts.org

I found that in Opera (10.62) the dynamic icon would appear while the page was loading, but would be replaced with the default when the page finished loading. I managed to fix this by changing the final line of the script from:

updateFavicon();

to:

window.addEventListener('load',updateFavicon,false);

...ie. add a listener so that it waits for the page to finish loading before it runs the script. (I did it this way instead of 'window.onload = ...' to avoid interfering with anything Google Calendar itself might be doing at window.onload). I haven't tried it in Firefox (or any other browser).

Hope that helps!