Just upgraded my Firefox from FF2.0 to FF3.0 today.  Here are my initial findings:

1) Browsing feels more snappier than FF2.0, definitely has improved memory handling.  Especially websites with flash content.

2) The most noticeable new feature was the ‘Awesome Bar’, which provides suggestions when entering the URL.  It takes time to get used to it, since it acts like a search box of your favorites/rss feeds rather than the most typed URL.  See here for tweaks of this.  Or revert back to FF2.0′s ‘Old Bar’ with this extension.

3) One minor issue, it doesn’t migrate my FF2.0 setting for “Keep history for the past x days”.  Lets hope all my other settings were migrated!

4) My URL bar doesn’t color yellow on HTTPS secure site.

To solve HTTPS bar coloring issue, see this, or if you’re on XP just add the following code in userChrome.css in your profile file, via C:\Documents and Settings\User\Application Data\Mozilla\Firefox\Profiles\chrome\

/* Secure site coloring */
#urlbar[level="high"][pageproxystate="valid"] > .autocomplete-textbox-container ,
#urlbar[level="high"][pageproxystate="valid"] > .autocomplete-history-dropmarker ,
#urlbar[level="low"][pageproxystate="valid"] > .autocomplete-textbox-container ,
#urlbar[level="low"][pageproxystate="valid"] > .autocomplete-history-dropmarker {
background-color: #F5F6BE !important;
color: #000000 !important;
}

Related Posts:

1. Add Search Engines to Firefox
2. Vacuum Database to Speedup Firefox
3. Viewing Firefox Cache Files