Personal preference first. Sure Chrome is slightly faster, but on my computer the difference is negligible. I'm sticking with Firefox, because of several features, but everyone has different needs. Here's my opinion:
Firefox's advantages:
1.) The "Awesome Bar" (Firefox's URL bar) is more efficient. If I visit Y!A a lot, I only have to type "y" into the Awesome Bar and the URL of Yahoo Answers instantly appears. Firefox 4 and up also allow searching in the URL area. The dedicated search box can be used to search Wikipedia, Bing, Yahoo, Amazon, Ebay, etc. On Chrome, the "Omnibox" (Chrome's URL bar) never seems to learn my most visited sites. I have to perform a new search every time.
2.) Chrome still doesn't support multiple taskbar previews in Windows 7. If I have two tabs open, I can only see one. It's sometimes annoying.
3.) The default size and layout of all buttons, toolbars, etc. is customizable without installing anything else. For those people who want a menu bar and tabs on the bottom, it's possible.
4.) If I close say 3 - 4 tabs, I can pick which one to reopen. In Chrome I can only reopen the last tab closed.
5.) Largest variety of add-ons of all browsers, so most customizable. If you want tabs on the side, extra security, password managers, etc. it's all available on Firefox. Chrome also has add-ons, but not as many.
Chrome's advantages:
1.) I can install it and forget it, because it automatically and silently updates itself. I also don't have to install Flash Player if Chrome is the only browser, since it is already included. This means less work, and reduces the number of confused people who don't know why their videos aren't working.
2.) Good set of features without additional add-ons, like the list of most visited sites that appears with each new tab.
3.) Search suggestions appear when you type in the URL bar.
4.) There's a Chrome Web Store where you can get and install apps.
5.) If one tab crashes it won't crash the entire browser.