Rated 4 out of 5 stars
I was looking for a replacement for FoxClocks after reading the performance data for addons from Mozilla, https://addons.mozilla.org/en-US/firefox/performance. This fit the bill nicely as all I have ever wanted was a lightweight replacement for the long dead Statusbar Clock extension.
The only missing feature is the ability to display localised dates as this uses the US format of Month/Day rather than UK format of Day/Month with no obvious way to change this e.g. Apr 6 instead of 6 Apr.