Here are the useful extensions for students.

Indic Input Extension 1.0
https://addons.mozilla.org/en-US/firefox/addon/3972

Girgit
https://addons.mozilla.org/en-US/firefox/addon/5483

Clustybar
https://addons.mozilla.org/en-US/firefox/addon/388

http://clickspeak.clcworld.net/
CLiCk, Speak provides point-and-click screen reading, which can be helpful for partially-sighted users or sighted users who have written language difficulties (such as dyslexia).

SQLite Manager
https://addons.mozilla.org/en-US/firefox/addon/5817

Quicknote
https://addons.mozilla.org/en-US/firefox/addon/46

Nuke Anything enhanced
https://addons.mozilla.org/en-US/firefox/addon/951

Chatzilla
https://addons.mozilla.org/en-US/firefox/addon/16

fireftp
https://addons.mozilla.org/en-US/firefox/addon/684

Web developer toolbar firefox
https://addons.mozilla.org/en-US/firefox/addon/60

1) Localized Software
2) Flexibility
3) Supports Old Hardware
4) Performance
5) Quality
6) Availability
7) Support
8) Cost
9) Security

Google Browser Sync for Firefox is an extension that
continuously synchronizes your browser settings –
including bookmarks, history, persistent cookies, and
saved passwords – across your computers. It also
allows you to restore open tabs and windows across
different machines and browser sessions.

By default, when you boot up the computer, Ubuntu will give you a login screen before you get to your X session. Many users are used to just being logged in automatically, and don't want to fuss with logging in each time they reboot their desktop.
To set this in Ubuntu, go to System -> Administration -> Login Window. You'll need to provide your password, then you'll get the Login Window Preferences window with five tabs. Choose the Security tab and click Enable Automatic Login. If you have more than one regular user, make sure to specify which user should be logged in automatically

http://www.linux.com/article.pl?sid=06/06/08/1651225

Does Firefox ever stall slightly when you begin to download a file? One possible problem could be that you've got more completed downloads than the Firefox Download Manager can handle. Hit Ctrl+J to bring up your recent downloads, and if you've got more than 20, clean them out.

For Firefox and Thunderbird, Mozilla enables a Safe Mode that loads the application without themes or extensions. If you've lost the included shortcut, you can start in Safe Mode by clicking the Windows Start button, then selecting Programs - Mozilla Firefox - Safe mode. If you notice a dramatic improvement, it's likely an extension or theme that's slowing you down. Disable them one by one until you find the culprit.

How do I delete autocomplete entries (history) inside the Search Bar ?

The Firefox search bar and some form fields on web pages have autocomplete dropdowns that appear with a list of previously-entered data. To delete individual entries, Click on the text area, press down to activate autocomplete, highlight the entry you want deleted, and press Shift + Delete.

You can clear the previous searches from the Search Bar. Just right-click it and select "Clear Search History".

You can disable the display of autocomplete entries by adding the following lines to userChrome.css
/* Remove autocomplete dropdown */
#PopupAutoComplete > .autocomplete-tree { display: none !important; }

Add YubNub to your Firefox address bar by typing about:config in the Location Bar then scrolling down the list and changing keyword.URL to http://yubnub.org/parser/parse?command= You haven’t lived until you’ve turned the address bar into a full-fledged command line.

One of the "features" of Firefox 1.5 is a pop-up dialog that appears whenever a page takes too long to load that reads. It’s not hard to delay this annoying dialog. To do so:
1. Type about:config in Firefox’s address bar.
2. Filter down to the value for dom.max_script_run_time.
3. Change the value to something higher than the default (which is 5.) I set mine to 20.

When you are looking for text in a web page using Firefox's Find as You Type feature, it will play a sound when the text entered can't be found. To deactivate this, enter about:config in the location bar. A list of all preferences will be shown. Look for preference "accessibility.typeaheadfind.enablesound". You can find it faster by typing a few characters in the Filter text box, for example "sound". Double click on the preference and its value will change to "false".