I made the switch to Firefox recently and I must say I'm impressed. I downloaded one of the early versions of Firefox when the Mozilla team first started working on it… years ago it seems. I thought it looked hopeful, but settled on Opera since it had everything I needed and more at the time.
I've been using Opera now for the better part of a decade and recently even switched up to the Alpha, now Beta, version: Opera 9. I liked the changes for the most part, but found the "Widgets" feature a little lacking and was having difficulty getting my Gmail to work in any version – though there are many alleged work-arounds and fixes. None seemed to work, however.
So I decided to give Firefox a try. I downloaded the browser and looked through the themes, plug-ins and extensions until I found a few I thought I would need, closed Firefox then restarted and viola! I'm using the Noia Extreme theme and have extensions like Paragrasp, IE Tab, Clippings, Adblock Plus, Spellbound, and Google Notebook installed.
Google Notebook was the main reason I made the switch, along with the need to open my Gmail. If you haven't tried it, Google Notebook is a very handy extension that allows you to create a private or public notebook on the internet that can be accessed from any computer with internet access. With the extension installed, Google searches have a "Note This" link along with "Cache," "Similar," "Translate," etc. You can also highlight text and in the right-click dialog there's an added "Note This" choice. The notes are then sent to your Google Notebook, where you can open them for edit; a handy feature for someone doing research on the internet. You can print, edit, delete entries or entire notebooks, etc. Saving citations and quotes from a journal article is a snap and I don't have to worry about whether my flash drive is plugged in or not.
Firefox & Google Notebook. Two champs so far.