I started using Chrome before I became a developer. I just found that it was faster, and I found it to be a better overall experience. Then with the increasing integration with my Google accounts pretty much cemented it. Now that I'm a front end web developer, I've tried the tools for all of the major browsers and prefer Chrome's dev tools because they're superior. The interface is better and I like the usability a lot more. Now more capabilities, such as writing to files from the console, are just continuing to cement it as superior for developers. There are also, I believe, more browser extensions for Chrome that make life as a developer way easier.

A friend told me once

"Give a developer a crap machine and they will write good code".

Which means that if a developer has a slow machine then they will optimise their experience with the machine to maximise efficiency/speed.

I will also say that my task bar consists of Chrome, Chrome Canary, Firefox, Firefox Nightly, Edge, IE, Opera as I do cross browser development in addition to server GUI access and if one breaks I have others.

Firefox is slow an unusable on some systems.

Integration - I have an Android phone and use my Google accounts on a different computers and mobile devices at the same time. I really need them to be in sync at all times.

Then there is a question of speed - Chrome, in my opinion, is faster than Firefox. And for a development, it has much better dev console.

I've been a Firefox user since before it was called Firefox, and also before it was called Firebird. I started using Firefox with Mozilla Phoenix.

Before Phoenix, Mozilla had an entire suite of internet applications: a browser, a mail client, an email program, and an HTML Composer. The suite was large, annoying to have to install to use the web browser, and the web browser was also slow. The Phoenix project was an attempt to break just the web browser out of the suite, and to create a fast lightweight browser with modern standards support.

The experiment worked…for a while. I switched to Firefox when it was the fastest and best. Unfortunately over time Firefox has gotten more and more bloated with features, and I find it quite slow. My switch to Chrome was due to a marginally nicer UI, but most importantly because Firefox had become just as unwieldy as the old Mozilla browser.

Over time Chrome has become bloated too, so now I use a little bit of Chrome, a little bit of Firefox, and a little bit of Safari depending on what I'm doing.

Chrome feels like home, Firefox feels familiar but awkward right now, and Safari is fast and had (until recently) awful keyboard shortcuts. Now it's usable :)

For me, because i see the more easy to integrate the google chrome extensions, the developers console and the look and feel, and i think at first the less memory usage.