For a person who deals mostly with the foreign currency or for someone who likes shopping a lot online, staying updated with the currency exchange rates is very important. Even I need to stay updated with the latest USD to INR rates for which I often check Google which takes time. If you also need to stay updated with the latest currency conversion rates then here is an extension for you.
The extension called Dcurrency is for the Firefox browser users only, using which they can get the real-time live currency exchange rates on their status bar. The extension is capable of displaying 3 currencies at the same time, with one of them being as standard. You can easily select the 3 currencies to be displayed according to your needs.
The add-on automatically updates the values every 15 minutes (by default) but this value can be changed to minimum of 1 minute using the add-on settings. You can also left click on the values to refresh instantly. This add-on uses Yahoo Finance as the source for the rates but if you prefer Google Finance more, then this can be changed too.
The add-on is also capable of listing the currency graph (one as shown below) observing which you can see the trend of the currency in the past. The graph can be useful in case you want to observe the past trend and guess the future rates.
If you find this add-on useful then you can download it from the link below. The only disadvantage of using this add-on is that it will show ads time to time, which you might find irritating.