While the awesome bar, download pause and resume, malware protection, the new themes, and serious performance improvements are perhaps the most representative features introduced with Firefox 3, here are some other useful ones you may not be aware:
As you may know, Firefox 3 introduces three different themes for all the officially supported operating systems: Firelight on Mac OS X, Tango on Linux, and Strata on Windows, which even comes in XP and Vista variations to better blend with Luna and Aero respectively.
If you are feeling envious of what the other platform or style got or just want to try a different look and have a couple of minutes to spare, you may want to give these themes a try.
Vista on XP, is a theme by Pascal Herbert that lets you use the Windows Vista theme, which is pretty much like the XP theme except all main navigation bar icons are blue and glassy instead of plastic-y.
If you prefer XP’s green plastic, try XP on Vista by the same author.

MacOS X Theme, created by GOLF-AT, brings Firelight’s brushed metal to users in Linux and Windows platforms. You will need a Mozilla Add-ons account though, as it is labeled experimental and awaiting further reviews.

Finally, if you don’t like change and believe Firefox 2 theme was just perfect, there’s also a theme for you: Firefox 2 for Firefox 3 will make you feel as it is 2006 again, yellow location bar for secure sites included.

Enjoy!
Do you know Mibbit? It’s an awesome web based IRC client. IRC, for those not old enough to recall, meant chat long before instant messaging entered the scene and is still a very reliable option for group and peer-to-peer text communication.
You can take advantage of Firefox 3’s support for web-based protocol handling to make it your default IRC client and handle irc:// links whenever you found one.
Mibbit added the necessary interface short before Firefox 3 final release and I’ve proposed it to be included with Firefox by default. But you can add it right now.
First, you will have to enable registration of protocol web handlers from different domains.
Now click in the link below to add Mibbit as an irc: links handler.
You will be prompted with a confirmation info bar. Press Add Application.
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You can now select Mibbit as your irc:// links handler from the Application page in the Options dialog.

Now when you click on irc: links a new tab with Mibbit and a tab connected to the IRC server and channel.
I suggest setting gecko.handlerService.allowRegisterFromDifferentHost back to false to prevent malicious web sites offering their own protocol handlers.
In case you need to remove Mibbit as an irc:// handler, go back to the Applications page in the Options dialog. Look for irc in the content type column. Open the menu in the Action column and select Application Details…, select Mibbit and press Remove.

Firefox 3 introduces real full screen mode where unlike Firefox 2 where the location bar and tab bar remained visible at all times, now they both automatically hide below the top edge of the screen.
If for some reason you prefer to see the location and tab bars, you can customize Firefox:
Or you can just turn off the toolbars slide up animation:
As with all advanced preferences you can reset them to their default values right-clicking and selecting Reset from the context menu.
Just in case, you enter full screen mode pressing F11 or selecting Full Screen in Firefox’s View menu.
Firefox 3 introduces full page zoom, that is, instead of just making text bigger or smaller, it resizes the full page including images and layout.
1. If you just want to zoom text, in the View menu, select Zoom and mark Zoom Text Only.
2. Firefox 3 remembers what zoom level you used for viewing pages in a domain and will automatically zoom them the next time you visit any page in the same domain. If you prefer Firefox not to remember it:
3. Another change you may quickly notice is that in Firefox 3 pressing Ctrl (or Cmd on Mac) and scrolling up and down, zooms the page in and out, unlike Firefox 2 and previous versions which used to work the opposite way.
4. By default when you press Ctrl + = and Ctrl + - to zoom in or out a page (Cmd + = on Mac), Firefox magnifies to 30%, 50%, 67%, 80%, 90%, 100%, 110%, 120%, 133%, 150%, 170%, 200%, 240% and 300%. If you want to define more or less fine steps or need to zoom to larger levels you can customize Firefox full page zoom:
Note that the zoom steps only affect zooming in and out with the keyboard or via View>Zoom>Zoom In/Zoom Out. Mouse scroll zooming uses its own steps but respects the maximum and minum zoom levels.
Also there seems to be no limit to the zoom level. I was able to set a 5000% cap and get a ridiculously large page.
While Firefox 3’s location bar is perhaps my personal favorite new feature and the one I missed the most when I have to use Firefox 2 for some testing, there are a lot of people who find it weird, obtrusive and don’t like it including bookmarks and history among its results.
An option to restore its old behavior was available for a few weeks during Firefox 3 development but it was pulled basically because it would need a lot of testing and it was thought it was not worth it. The option may come back for Firefox 3.1.
In the meantime, for those who prefer the old way and those who want even more power, here are 9 easy tweaks you can try.
1. Make the autocomplete menu show only typed addresses and not visited or bookmarked
2. To set the autocomplete menu to single line suggestions install the oldbar extension, developed by Seth Spitzer. Together with the previous tweak pretty much restores Firefox 2 behavior, except typed characters are searched in all the address instead of just the beginning.
3. Change the number of suggestions displayed in the autocomplete menu
4. Hide the star button if you prefer to use the Bookmarks menu or a keyboard shortcut (Ctrl + D)
5. Always show the Go button. By default it is only displayed when you are editing the current web address.
6. If you enter firfox in the location bar and you try to correct it, the autocomplete menu won’t suggest anything because it only keeps working as you edit the last characters. Install the Edit Middle extension, developed by harikaried, to make it work with edits anywhere.
7. To auto select the first suggestion in the autocomplete menu, install the Enter Selects extension, developed by harikaried. You will need to logon to Mozilla Add-ons to install it as it’s still experimental.
8. Tweak the autocomplete menu title and addresses size and colors by adding these lines to your userChrome.css file. Check for the specific hexadecimal color code to use at WebMonkey.
.ac-comment {font-size: 100% !important; color: #444444 !important; }
.ac-comment[selected='true'] { color: #FFFFFF !important; }
.ac-url-text {font-size: 100% !important; color: #000077 !important; }
.ac-url-text[selected='true'] { color: #FFFFFF !important; }
9. To include Google and Amazon search results in the autocomplete menu install the Searchery extension, developed by Ian McKellar. You will need to logon to Mozilla Add-ons to install it as it’s still experimental.
10. Bonus tip courtesy of Frederick from the comments: To hide the web feed icon from the location bar, add this line to your userChrome.css file: #feed-button[feeds] { display: none !important; }
Happy tweaking!
Thanks Jens, Marius, and Marcelo for the suggestions and corrections which work better indeed. There were unwanted spaces and wrong quotes in the original post but have now been corrected.
A common complaint about Firefox 3’s location bar is that the autocomplete menu is too long because of the big font sizes, that the page title grabs too much attention compared to the address or that the address is too difficult to read.
While the default colors and sizes is still under review, you can tweak it right now to better suit your taste. Just add this code to your userChrome.css file:
.ac-comment {
font-size: 100%! important;
color: #444444 ! important;
}.ac-comment[selected=”true”] { color: #FFFFFF !important; }
.ac-url-text {
font-size: 100% ! important;
color: #000077 ! important;
}.ac-url-text[selected=”true”] { color: #FFFFFF !important; }
.ac-comment refers to the title styling which I have changed to be the same size (100%) as the address and a lighter gray. .ac-url-text refers to the address which I have set to blue.
It looks like this now:

You can play with different font-size values and proportions and colors. For color codes, check W3Schools.
You can also reduce the number of suggestions in the autocomplete menu with this tip.
Update: Added CSS code to change the text color when selected. Thanks David.
While the new location bar is currently voted the favorite Firefox 3 feature with about 37% of 1,695 votes cast so far, it seems from comments to my recent Firefox 3 Beta 3 review, that a significant number of users are less than happy with it.

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