SMF 2.0+ Modification. I will not back support this mod to older versions.
This modification adds a unread PM counter to the favicon. In addition it continues to check for PMs at a specified interval. Setting this variable to lower can result in server degration/performance issues. Use with caution. The default timeout is 1 minute (60 seconds).
Prior to asking for support, check out the wiki: https://github.com/jdarwood007/smf-unreadPM_count/wiki
Credits for this ability go to Tom Moor for creating Tinycon: https://github.com/tommoor/tinycon
Browsers that support this:
The following browsers will fall back to changing the title due to lack of support for this:
Internet Explorer 9