EDIT: The Chrome extension has been reviewed and accepted in the Chrome Webstore!
If you're interested in trying it out, click here.
Even though this question is 10 years old, I am astonished to see that no tool has been created to solve this problem, so as a young creative web developer, I created that tool, it's called My Web Shortcuts!
It's an open-source & 100% free browser extension used to create custom shortcuts for the web. I hope this helps.
At the time of writing this answer, it's being reviewed by the Chrome Webstore team and isn't available on the Webstore yet. So you would need to install it manually from the GitHub Repo. You can go to releases and download the zip file of v1.0.0, unzip it, and drag the whole folder of extracted files into the extensions manager in your browser.
Only Chromium-based browsers (Google Chrome, Brave, Opera etc.) are supported at the moment.
Please note that it's the first version and you may face a few bugs, so if you find one, please create an issue for it.
altD
while on Facebook it will automatically clear all new notifications. And have the user set these shortcuts themselves.