Apparently, when Firefox is opened it draws the window, then the browser interface, and finally the homepage. Chrome on the other hand, draws the window and browser interface simultaneously, and then it loads the website. In Hill's words, "Firefox feels very sequential in its loading, while Chrome seems to do everything at once."
Additionally, Hill says that Chrome places less of a visual emphasis on the webpage loading icon, whereas Firefox's is in plain sight not to mention that Chrome's icon animation rotates faster. Chrome also hides website titles until a page is mostly loaded, whereas Firefox shows the title more quickly making it seem like users have to wait longer.
All of these things apparently add up and give the illusion that Chrome is significantly faster, and Hill says Firefox can be tweaked similarly. Head over to the full blog post for more information, including a few data graphs illustrating the speed differences between Firefox and Chrome.