Great but... Rated 4 out of 5 stars

Very useful addon, have been looking for something like that, however it very hard to pick different shade of the same colour. In Photoshop for example you can open colour picker and click on small B beside to bring up a slider to make the colour brighter or darker. Please see screenshot below. I'd love to see similar option in Firepicker.

This review is for a previous version of the add-on (