Unimpressed Rated 2 out of 5 stars
Not a complicated extension, but this just doesn't work well. Most apparently, there are no flag icons as pictured, and no GUI method to enable them. Worse is the way the extension ignores changes to its configuration, creating duplicate entries in prefs.js instead - which confuses the extension and locks it out. Fortunately I can live without itThis review is for a previous version of the add-on (2.3.14).
How to show flags
To show flags in your statusbar, open the main FoxClocks window (double-click on a statusbar clock), then select all the clocks in the Watchlist and press F2. Alternatively, you can show/hide each location's flag individually from the 'Display' tab of its 'Location Properties' window (double-click on the location in the Watchlist to open this window).
Problems with configuration not 'sticking' are usually down to a corrupt Firefox/Thunderbird profile.