This section contains addons (themes and extensions) written for the Mozilla-related SeaMonkey and Firefox products. Addons come in 3 main varieties.
Extensions are major addons that add significant functionality to the browser. They usually go beyond just look-and-feel and actually change browser behaviour in some way.
Themes will significantly change the look-and-feel of the browser, usually moreso than the more lightweight (and also more recent) 'Persona' addon type.
Search providers are additions to your search box on the toolbar. They allow you to search on various different sites and search engines, for whatever the site/search engine allows you to search for - from books at Amazon to Google French language to Bugzilla bugs.
Firefox no longer provides the kind of comprehensive browser interface that Firefox 3 did, and this is by design. SeaMonkey still does, and this is because of a more conservative approach taken by the SeaMonkey project to modifying their interface that is unlikely to change.
SeaMonkey is a suite of internet software applications, at the heart of which is a web browser akin to Firefox.
With the (imminent) release of Firefox's new "Australis" design, the Firefox project's developers have (by their own reckoning) fundamentally changed the browser. TechCrunch reported the following from Jonathan Nightingale, Mozilla's Vice President of Firefox engineering:
"Maybe we shouldn't even call it a browser anymore. 'Browser' is really an antiquated word. People don't really browse all that much anymore." Instead, he argues, we now mostly use our browsers to access sophisticated web apps, web-based productivity tools and social networks.
(source: TechCrunch, 2013-06-21)
Some of us disagree, and would like to keep using an actual web browser. This fundamental change to Firefox is one that minimizes the browser interface (or "chrome"), in favour of maximizing "real estate" for the contents of tabs. This may be good for those who only use so-called web apps, but for some who use the web more comprehensively (and/or have a large PC monitor and not so much need to maximize screen "real estate"), it is a highly undesirable change. Various aspects of a comprehensive browser chrome are very useful for a web developer or advanced user, such as a permanent status bar, and a tabs-on-bottom layout that results in these toolbars staying around no matter what content is loaded in a tab (with a tabs-on-top layout, these toolbars are sometimes removed when the browser wants to present content in a way that the developers consider doesn't warrant any browser toolbars). There are also various minor unfortunate changes that have been made to the Firefox interface, such as the inability to focus on a tab with the mouse, and the (by default) cramming of full menu bar advanced functionality into a single dropdown button in the corner. In addition, Firefox's interface has gone in a highly "minimalistic" direction that many users don't like, resulting in an interface that (whether on purpose or by accident) looks very similar to the Google Chrome browser, even down to the icons used sometimes looking almost identical. Large, colourful toolbar icons are out, and small, monochrome ones are in. This is bad for accessibility and (this is a personal opinion) just plain ugly. The days of Firefox 3's interface are long gone.
That is, except for the SeaMonkey project. SeaMonkey is a community project, closely tied in with Mozilla Corporation, that was forked from the old Mozilla application suite at around about the same time that Firefox development was getting into swing. Because of a much more conservative philosophy towards modifying the application interface, SeaMonkey's browser interface is still similar to the interface at the time it was forked - rather like Firefox 3. Firefox's interface, however, has undergone massive changes culminating in the aforementioned "Australis" design.
Ironically, this means that SeaMonkey's interface is now far closer to Firefox 3's than Firefox's is, and therefore using SeaMonkey's browser (themed and tweaked with the addons you will find here) is the best way to get a Firefox 3-style web browsing experience with a comprehensive browser chrome. Firefox could perhaps be "modded" back to what it used to be with an enormous amount of work via extensions, but at this point it would be swimming against the tide. The Firefox developers are clear on what the Firefox interface is going to look like, and it's nothing like the Firefox 3 interface. Any attempt to modify the Firefox interface back through extensions will require constant maintenance to deal with regular interface changes made by the Firefox team (who will not be at all interested in maintaining compatibility with these extensions).