Yeah.. It might be because there are n number of add-ons available in mozilla with which we can do task quickly. This facility is not available in Chrome or IE.
I couldn't find even google toolbar for Chrome. Most of the webmasters enjoy Firefox and its Addons especially "nodofollow" and SEOquake.
Not as many SEO features / Addons for Chrome or IE. They are still used widely, but for SEO and such, Firefox is the way to go right now. I use chrome as a backup.