Can I remove the countdown when installing extensions in Firefox?

When installing an extension in Firefox, the confirmation dialog makes you wait 5 seconds before you can install the extension. I find it annoying and unnecessary, is there a way to shorten or remove the countdown so I can install extensions without waiting?

I found this:

You can easily disable the installation wait by a simple "about:config" modification.

1. Type about:config into the Firefox address bar and hit enter.

2. Click on "I'll be careful, I promise!" button.

3. Enter "security.dialog_enable_delay" into the Filter text box.

4. Double click on that preference value and change the value to 0

Yes, you can. I've done this once. Unfortunately right now I can't remember how.

UPDATE: Got it: https://addons.mozilla.org/en-US/firefox/addon/mr-tech-toolkit/developers

Just install this extension (and restart) and alongside with other features you'll get offered to remove the countdown next time you click to install an extension.