Pt 1 & 2 is here (Turbo Speed and Less Memory, Full Page Zoom and Drag everywhere): https://forums.macrumors.com/threads/459507/
Pt 4 is Here (Password and Download Manager) https://forums.macrumors.com/showthread.php?p=5289233
Pt 5 is here (All the rest) https://forums.macrumors.com/showthread.php?p=5423938
5. Awesome Bar
the location/address/url bar of firefox 3 is dubbed awesome bar, for some good reasons. Lets take a look at it.
Dropdown history, click to show your most visited 12 pages.
Star button, one click to bookmark current page!, click again to customize it: move to certain/new folders, remove it, add tag(s) (Tags can be a search term in your urlbar input)
what you do: type in any number of strings (1-oo)
what firefox will response:
Perform instant search in your history and bookmarks looking for the matches from title bar of the page, url of the page, or the tags you assigned to your bookmarks when you added them. Sorted matches result according to the visit frequency.
Security, are you worried?
Firefox 3 is more secure than version 2. Take a look:
Click the site favicon in the location bar to see who owns the site and to check if your connection is protected from eavesdropping. Color is used to remind you the status of the current page.
sites which are known to install viruses, spyware, trojans or other malware.
pages suspected as web forgeries.Firefox will inform anti-virus software to check the file after downloading executables (windows only).
Next to Come: Ease of use, Passwords and Download Manager.
Pt 4 is Here (Password and Download Manager) https://forums.macrumors.com/showthread.php?p=5289233
Pt 5 is here (All the rest) https://forums.macrumors.com/showthread.php?p=5423938
5. Awesome Bar
the location/address/url bar of firefox 3 is dubbed awesome bar, for some good reasons. Lets take a look at it.

One by one from left->right are: favicon, urlbar, RSS button, Quick Bookmark button, Dropdown History (downwards triangle)
Site info button (favicon), it displays site icon as firefox 2, but also provide security information with different colors, detail in next section.
Dropdown history, click to show your most visited 12 pages.
Star button, one click to bookmark current page!, click again to customize it: move to certain/new folders, remove it, add tag(s) (Tags can be a search term in your urlbar input)
click star!
click Again!
urlbar, here, it acts like a spotlight search for your history and bookmarks, 
click Again!

what you do: type in any number of strings (1-oo)
what firefox will response:
Perform instant search in your history and bookmarks looking for the matches from title bar of the page, url of the page, or the tags you assigned to your bookmarks when you added them. Sorted matches result according to the visit frequency.
Ever have 100, 200, 500+ bookmarks and can't find what you want from the list? No MORE! 
Input tags you assigned to your bookmark
Input one term
Input two terms
Input 3 terms (bookmarks sorted higher than history, as you can see.
PS. You can ignore the matches results and just press enter after input, firefox 3 will just perform google and/or feeling luck like firefox 2.
no matter its your previously visited websites (history)
or its you interested websites (bookmarks)
even if you only remember part of the title of the page
even if you only remember part of the url of the page
even if you only remember the rough category you used (tags)
Type and spotlight, awesomebar is ready for you!
PS. urlbar still retain the function as a google feeling luck search field. e.g., type "caltech parking" in urlbar and press enter, you will be redirected to http://parking.caltech.edu/ , (will goto a google search page if no sensible result can be found...)
6. Security in a Box
Input one term

Input two terms

Input 3 terms (bookmarks sorted higher than history, as you can see.

PS. You can ignore the matches results and just press enter after input, firefox 3 will just perform google and/or feeling luck like firefox 2.
no matter its your previously visited websites (history)
or its you interested websites (bookmarks)
even if you only remember part of the title of the page
even if you only remember part of the url of the page
even if you only remember the rough category you used (tags)
Type and spotlight, awesomebar is ready for you!
PS. urlbar still retain the function as a google feeling luck search field. e.g., type "caltech parking" in urlbar and press enter, you will be redirected to http://parking.caltech.edu/ , (will goto a google search page if no sensible result can be found...)
Security, are you worried?
Click the site favicon in the location bar to see who owns the site and to check if your connection is protected from eavesdropping. Color is used to remind you the status of the current page.
Normal Color: no security method is used
Blue: Transfer of data with current webpage is encrypted with SSL, TLS, etc, the page is verified by network security firms
Green: Current page is certified by EV (Extended Validation)
PS. Click the favicon (any color, anytime) will give you more information about the website.
PS2. The Cop's name is Larry in case you want to know
Firefox 3 will display a warning page you when you try to visit dangerous websites such as:Blue: Transfer of data with current webpage is encrypted with SSL, TLS, etc, the page is verified by network security firms
Green: Current page is certified by EV (Extended Validation)

PS. Click the favicon (any color, anytime) will give you more information about the website.
PS2. The Cop's name is Larry in case you want to know

sites which are known to install viruses, spyware, trojans or other malware.
pages suspected as web forgeries.Firefox will inform anti-virus software to check the file after downloading executables (windows only).
Next to Come: Ease of use, Passwords and Download Manager.