The oyoy.eu search engine Firefox extension is a little tool I made mostly for myself to help me with finding out more about a website. It contains just about all the necessary online (and free) tools that are needed for a site and domain check.
Installation is simple: just click here to install (you may have to give permission to install it and then re-try that link).
Usage is fairly self explanatory, after re-starting Firefox you will have a toolbar (which can be turned off) and a context-menu. Just go to a page on the site you wish to check and use the functions. Most tools will open up a new tab and run there. This lets you use a few of the functions to start with and then check them separately. The tools are mostly from this website (and a few others).
Functionality:
Current versions: