Using the FireFox browser has had one many hassle for me.  If it could not connect to a site you are browsing to, it would popup an alert popup dialog that says it cannot connect.  Most browser will simple display an error page.  

The problem is that if you are going to the site in a new window, the URL you tried to go to will not be in the browser so you cannot hit refresh.  You have to enter it again.  This can be a pain when you have any problems with sites.

To make it so that window does not show up you can do the following steps:

1. Browse to about:config (if you didn't know, this is the all-options-available, no-docs config for mozilla)

2. Find the line that begins with browser.xul.error_pages.enabled

3. Select this line and hit enter (value in last column should change to true and line should become bold)

4. You're done. Try browsing to a page that does not exist and watch in awe as a message box does not appear.