password reuse
Today using the same username and password over and over it’s definitely the quick way to weaken your security online; too bad that it’s nearly impossible to keep track of every password and it’s reuse rate in a standard browser, although this is an addressed problem.
I made a very simple addon, just a proof of concept of what the functionality should be. Enter your user and password combination and it will pop your statistics about that combination reuse.
Here’s the repo if you know how to build addons from source or do you want to contribute, I will post the link to the addon page on addons.mozilla.org as soon as it will be approved by Mozilla.