Firefox is very easy to personalize via configuration files. I've found the
userPref.js files to be surprisingly capable, I've added them as well as my bookmarks file to my dotsync for a (very) minimal Firefox UI footprint (pictured).
The original post follows.
The web is my platform of choice. It really boils down to simplicity in boxen hopping. I routinely jump between my laptop, home desktop, home server, work desktop, work server, and whatever other computers I happen to be building or working on at the moment. Having consistent configurations in all those locations is critical to getting any serious work done. If I need a calculator I don't want to worry about starting Windows calc or using a Dashboard widget or Calculator.app or hoping that bc is installed on whatever UNIX I'm using; my preference is to hit ctrl-k and use Google Calculator because it's the same for any Firefox installation. Google and Firefox Quick Searches play a large role in making the web a viable platform.
My productivity is based on two environments, Firefox and a terminal. The terminal environment is easy to keep up-to-date and synced between disparate computers due to the wonders of scripting and so-called dotfiles. Firefox, on the other hand, isn't as simple to keep consistent. I tend to be a purist when it comes to extending most software, I dislike installing extensions or plug-ins especially when each new release of the base program requires updates to the add-on. Although Firefox is fairly decent at automatically updating extensions, and with the up-and-coming 1.5 release decent at updating itself, sometimes it corrupts preferences or an extension author is late to release an update. When I install a fresh copy of Firefox on a new computer my bookmarks is the only file that is easily put in place since the prefs.js file is littered with extension-specific lines.
Unfortunately there are a few Firefox extensions I simply cannot live without and I feel strongly that all of these unless otherwise noted should be the default behavior for Firefox.
Opera does this, and has for some time. All browsers need to allow complete and instant recovery from crashes. This extension will save your window positions, tabs, and even what you were typing. It is imperative that this be built into vanilla Firefox.
Firefox both introduced and hooked me to tabs, yet of all the tabbed browsers Firefox is strangely the least configurable and the least usable without resorting to extensions. The default behavior of having one close tab button on the far right that only works for your current tab is a minor usability issue, this little extension gives a close button on each tab. Safari got this right from the beginning and pulled off near-perfect tabs with only three checkboxes in the preferences.
I really appreciate being able to quickly traverse up a web directory tree. Safari's solution is especially elegant; if you Command-click the window title it will bring up a quick menu. This extension also allows you to navigate using the increasingly used rel header tags. Why let people with disabilities have all the fun?
Web applications are starting to come of age, yet the input methods browsers employ are two decades in the past. ViewSourceWith allows you to use an external editor for textareas which will continue to be useful until browsers modernize, a native spell check may be a good start. I use Vim. (Note: this extension seems to have replaced the seldom-updated MozEx.)
The Web Developer Toolbar is critical to my professional work. However, since I'm not always at work it doesn't need to be installed on every computer I use. Therefore I will make an exception to this extension since I don't mind installing it occasionally.
Unfortunately this extension is a must on the Macintosh otherwise Flash-heavy sites can make your computer completely unusable. This extension lets you start Flash animations selectively. Again, this extension deserves exception since it is hardly Mozilla's fault that the OS X Flash player sucks.