Installing extensions into a new SeaMonkey install this morning, I got quite a shock!
Simple Clocks :: Add-ons for SeaMonkey
This add-on has been removed by its author.
As someone with friends in multiple timezones, Simple Clocks was the simplest way to see at a glance whether or not I'd be waking anyone up with my tweets, newsgroup messages and the like. It's a shame the developer couldn't keep it going.
I guess it's back to FoxClocks; another excellent plugin but with extra features I don't really need.