Remove permanent redirect (HTTP 301) cache in Firefox

As a web developer configuring SSL certificates on websites you deliver, as we do, you might be faced, one day, with a small issue about configuring a 301 redirect from HTTP to HTTPS that has to be reverted. It so happens that browsers *really* take it to heart to cache an HTTP 301 (permanent redirect) message seriously and deeply. So much so that it might become very difficult to remove this redirect and ever be able to access the site in HTTP again. Well, there's a solution to that, and it's documented on the Mozilla support forum. Basically, open your browser's history window, search for the site (in all its forms: https or http), select the site in one of the results and click right to "Forget this site". Don't forget to first close all tabs that would currently be opened on the site to be forgotten: this procedure won't work if you don't!