Very simple yet effective layout. Minus one star because the cursor moves on the left side of the calculation. This makes it impossible to clear the row via backspace, or delete.

Super prática! Eu realmente gosto da calculadora !

I would give it 5 stars if you could use parenthesis when calculating.
Even a simple calculator needs it.

Trying adding other modes like programming, scientific advanced etc.

At last, one calculator add on that works!!!
Is it possible for you to add a history of calculations and that can be viewed even after a restart of Firefox?!? Also with that if possible to take advantage of past calculations and re-use them...