I decided to switch to firefox for a week to try it as my main browser. (I used to use firefox years ago) Here are a few things I've noticed.
In linux both firefox and chrome seem ok, chrome looks much better on larger fonts as firefox seems to space out each character when scaled (not sure if intentional but it looks poor).
In windows I noticed a huge difference. Chrome looks so much better, firefox seems to stretch fonts. This is seen even more when using the font-weight attribute.
Here is an example of font rendering in windows (firefox top, chrome bottom):
I guess a lot of people wouldn't notice this but as I was working on website development using firefox, things just didn't look right (even on linux).
I found equivalent extensions for both browsers so don't really see one as having an advantage.
I feel firefox wins on this as private browsing has extensions enabled on firefox, they seem to be disabled on chrome. This may be beacause on chrome some extensions may leak data?
I have only used firefox for a week & have found the developer tools ok. Both chrome and firefox seem similar. One thing which is really annoying about firefox is when you right click a component you cannot copy it direct (options are "copy inner html, copy outer html).
This is possibly specific but the H264 plugin that comes with firefox doesn't seem to work on my linux. Also when trying out new HTML5 elements I noticed firefox doesn't support some, although this is possibly because they are so new. (firefox scores 462 out of 555 points on html5test.com & chrome scores 523)
Other Things Of Note
I found setting up RAM cache on firefox easier (just took a few tweaks) Firefox also uses a prefs.js file for settings which can easily be used when creating new profiles.
On android I have found firefox much faster & stable (which is really weird)
I'm not sure if I can put up with the font rendering in firefox. The developer tools on chrome just seem better/easier to use. Overall both browsers seem pretty quick.