Firefox 3.1 has Web Workers (threading) and Geolocation· 2 minute read
Geolocation is an interesting one for services like Twitter, Jaiku and possibly Facebook as it would allow users an easy way of updating all the services with their current location simply by Firefox broadcasting the information. But even more interestly Yahoo! and Google maps (or a custom implementation of them – I am tempted but do not have the time at the moment) could use it to real time track the location of a user. So potentially you could use the maps like a satellite navigation application with the watchPosition() function all the user would need is a GPS mouse with a Firefox plugin to read the position from it. Oh yes and of course they would need a laptop with Firefox installed on it and a mobile internet connection. :-)
Obviously for any of this to work you will need to be running the latest beta available from the Mozilla site.