The keys don't have to be the first letters of the addresses of the sites you visit. It can be any letter included in the address. For example connect.garmin.com can work well with either 'c' or 'g', depending on your preference.
In Firefox, once your browser has been made familiar with the sites that you regularly visit, a process that can take from a day to a week, depending on how often you use the web, just type in the first letter of the website you want to go to. Firefox will immediately give you the most visited site beginning with that letter. Now, just touch the arrow cursor down for one click and press enter. This is very quick, depending on how you usually navigate the Internet.
In Safari, the greatest improvement is that you actually don't have to press the arrow key at all. Safari will display the most visited site with that letter directly in the URL bar. This means that you only have to push the enter key to navigate to it. This might seem like a small improvement over Firefox, but it is so much more convenient. We wish that all browsers did this.
Chrome works the same way as Firefox, you'll need to push an arrow key after the right URL has been displayed and then press enter. If one key doesn't work in the beginning, you can try using two, the first two letters of the address. The more you associate one key with one URL, the more your browser will display that URL first before anything else.