For this extension to be effective, all the developers working on the project that the review is being made should have this extension installed.
The reviewer can use the extension like this:
When commenting on Bitbucket, the reviewer should first add this string customdiff, followed by 2 code blocks, the first one stands for what should be removed, and the second one for what should be added/refactored from the old diff. This is illustrated on the image bellow.
Enjoy using this!