Hi

I do not believe that this question is to do with the Firefox web browser, but I will try to help.

Unless you have an original unaltered copy of the picture, you will need to use some photo editing software. A popular free open source package is The GNU Image Manipulation Program (GIMP). It is a freely distributed piece of software for such tasks as photo retouching, image composition and image authoring. It works on many operating systems, in many languages.

I hope this helps.

Use the same program that you used to add those colors to the image to remove them?