I Love It; But ... Rated 4 out of 5 stars
I love this addon. It saves me tons of time changing the text on pages so that I can see the text. One problem that I've been having (I'm using FireFox 22.0) is when I perform a Google search, the search closes up so that the results are not visible. The only way to make the search results visible is to disable the addon and reload the search page again. Don't know what's causing this; but, it would be nice to be able to exclude certain pages from Blackening.This review is for a previous version of the add-on (188.8.131.52-signed).
Have you installed the toolbar button? There is an "Original" menu button to restore a page to its original state. You can install the toolbar button by right-clicking on a toolbar and selecting Customise. The button is the one with a big black B.
There is a problem with the top-most menu on Google's page which will only be fixed by excluding this page as you suggest. This is on the cards for a future version.