It works in FireFox(i.e. Gecko) just as well as in other browsers. However, StartSsl is slow to update their OSCP entry for your site. As FireFox uses this to see if your site is absolutely safe, it takes +- 24 hours after getting one of their certificates until  FireFox will display it properly.


Although their site is a little clunky, I really like StartSSL and their service. I've been using the free certificate for https://last-mail.org, where it works perfectly.


About the tutorial:
-You do not need Google Chrome at all to perform these steps.
-Many web servers have a hosting packet such as cPanel, which greatly reduce the amounts of steps to take. There are also tutorials available on the site of StartSsl itself.