The interface itself didn't change much, except for a small change here and there, like the address bar or the way the add-on manager handles newly installed themes. The add-on manager will show recommended add-ons, allowing you to select first from a bunch of add-ons you probable didn't even know they exist.
Firefox, using default theme and running in GNOME 2.22
One of the best things I like about Firefox is the password manager and the way cleaning privacy history and cookies is handled. For example, you can set the password manager to remember all the passwords and usernames you enter in forms, and set the privacy manager to only clean up cookies, browsing history, cache, authenticated sessions etc, without deleting the passwords. This way, even though you cleaned up all the cache and cookies, Firefox will still remember usernames and passwords.
Cleaning up private data - you can select what you want to keep
After installing a new theme, the add-ons manager will automatically select it and offer a Restart Firefox button so you can start using it. You have the option to let Firefox remember the last used tabs so it can load them again after the restart.
Firefox add-ons - new theme is used automatically after restart
After the successful launch of Firefox 3, which benefited of around 8.4 million downloads, several news websites reported that a critical security issue was found in the 3.0 version, allowing code to be executed with user permissions on the host computer.
The official website offers several pages showing the new features in Firefox 3.0, like this one. Well, the password manager is not a new feature, I know this one from way back in Firefox 1.x. As Mozilla provides, other new features would be smart location bar, full zoom - by using CTRL++ and CTRL+-, you can zoom in and out of a web page, a very nice feature if you really need it - one use I can think of is the case in which the fonts are too small and you haven't set yet a minimum font size. It probably helps websites not so well designed which offer horizontal scroll too (you know, those annoying websites which make you scroll horizontally in order to read the whole line to the end). You can zoom out on those and read them all at once.
The address bar
Regarding the speed, Firefox looks to load faster (or is just a false impression?), but the interface reaction is as slow as it was in previous versions. Mozilla says the Gecko layout engine (used to render web pages and the Firefox interface) was improved and it is now faster.
Using the Past Modern theme for Firefox 3.x
As for documentation, Firefox 3.0 currently offers help online, on the official website, contrary to Firefox 2.x, which also offered a comprehensive and easy to understand offline help.
Overall, Firefox is what it already gained throughout the years: the most popular browser on Linux. I couldn't even think that 3.0 will be anything but a good release, even though with one great accomplishment (the big number of downloads), also came a security vulnerability.
Updated: Jun 22, 2008 (Created: Jun 22, 2008)