Firefox is a safer browser than IE or Chrome primarily because of two add-ons, NoScript and AdBlock. NoScript uses a whitelisting strategy so that no script can run without the user explicitly allowing access from a specific site. AdBlock simply removes ads from view, which eliminates the possibility the user will accidentally click on an ad and be deposited on a malware or spyware site. I have installed these two add-ons on all of my desktops and consider them to be standard equipment for all computers that I provision.
I do not install Chrome on any machine. There is no reason to have two tools when one is better by every measure than the other.
There should never be one-click access to IE. Typing should be required. If I see IE on a machine, I delete the icon and remove it from the Start menu. IE should only be accessed by experienced users on an as-needed basis for updating Windows and nothing else. In Windows XP on my desktops, it can be accessed by choosing to run a program and then typing in "iexplore.exe". As soon as the necessary task is completed, IE is closed.
The reason IE is bad is an old one. It was true in the 1990s and it remains true today. IE is the browser with the largest market share, so it has "target" written on its forehead in bright red letters. Another problem is that it is the default browser in Windows, so the biggest number of clueless users will be using IE. Effort is required to install Firefox, though much less effort is required to install Chrome, because these days it is included by default in tons of applications from Avast antivirus to the kitchen sink. Google is paying software vendors to include Chrome in the installers. The result is that Chrome will be grabbing more of the clueless user population. The reason elite users stick with Firefox is they like customizing their browser and they have a deeper knowledge base that allows them to do so. All of these factors make Chrome and IE the top targets for black hats, who know quite well that clueless users make easier targets.
Among my friends, I have heard of many people getting hacked while using IE exclusively. They wind up spamming all their friends, losing money, losing their credit rating, or having to reinstall Windows altogether. I have not heard of many people getting hacked that use Firefox. Maybe it is because the people that use Firefox also take other precautions, or maybe there are other reasons involved, but I am sticking with Firefox until the bitter end.