Calculator is a complete scientific calculator that is integrated on Firefox as an extension; it is also available for Thunderbird.
You can open the calculator as a new tab, make it visible on Firefox's side panel, or open a new Firefox window for it. It also keeps a long history of previous operations.
On the menu, you can find numerous constants and fixed values, as well as frequently used functions. It is also worth noting that it comes with many measurement units with which you can quickly carry out conversions.
If you want to integrate a calculator onto your browser then you should try Calculator, you will surely be impressed.