Advanced section - General tabAccessibilityAlways use the cursor keys to navigate within pages - the webpage will scroll down line by line, instead of page by page. You will also see a cursor key if you enable this option.
Search for text when I start typing - Firefox will start searching once you type.
BrowsingUse autoscrolling - for those who are using a mouse with a scroll wheel, and you don't fancy scrolling all the time, check (tick) this box. This allows you to click on the scroll wheel, and scroll down the pages as fast or as slow as you want.
There will be people who don't like this feature, especially if you misclick a lot of times.
Use smooth scrolling - smooth scrolling allows the smmoth moving of pages when you scroll down a page, especially when you use the Page Up or Page Down button. The page doesn't suddenly jump from one page to another.
Check my spelling as I type - checks your spelling and underlines it in red when your spelling is wrong. The dictionary used is an American dictionary, so you will get warnings about your spelling errors when spelling in British English, the English language used in Singapore. To do so, install this
British English Spelling Dictionary and set it as the default dictionary to be used.
Choose your preferred language for displaying pages - self-explanatory. Just choose a language that you want. English/United States (en-us) works fine for most of us.
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Advanced section - Network tabConnectionConfigure how Firefox connects to the Internet - this is more for advanced users. By default, Firefox connects directly to the Net.
You can change the way Firefox connects to the Net by clicking on the
Settings... button.
Direct connection to the Internet - that's the default, and not to be changed unless you are having connections problems.
Auto-detect proxy settings for this network - use this option if you know your ISP is using a proxy server, or your ISP requires you to connect via their proxy server before connecting to the Net.
Manual proxy configuration - this option is for those who are complaining of slow Net speeds. For Singnet users, here's how you configure it:
HTTP Proxy: proxy.singnet.com.sg Port: 8080
No Proxy for: localhost, 127.0.0.1
All the other fields are blank.
Starhub and Pacnet users, I don't know. Anybody who knows can share.

Automatic proxy configuration URL - no idea what this function is. But is most probably not used by average users.
CacheStores the webpages you've viewed in your hard disk. For those who have slow connections, it's better to use the cache, or you'll have to load everything from the server, which is going to take a very long time. For those with fast connections, set this to a low value or don't use it is up to your own preferences.
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Advanced section - Update tabAutomatically check updates to - check for updates
By default, Firefox and Search Engines boxes are checked. If you don't want Firefox to check for updates, untick the boxes.
When updates to Firefox are found:
Ask me what I want to do - Firefox will tell you about the updates and ask you what to do.
Automatically download and install the update - it will download and install the update when you open Firefox.
The
Warn me if this will disable any of my add-ons will make Firefox warn you when the update makes any of your addons incompatible with Firefox.
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Advanced section - Encryption tabProtocolsUse SSL 3.0 - Use Secure Sockets Layer Level 3 encryption, for communicating securely with websites. This is a common protocol used by banks, or any sites that needs you to transfer money.
Use TLS 1.0 - TLS is Transport Layer Security, is another encryption protocol similar to SSL. Some websites use TLS 1.0, so if you disable this option, you might not be able to visit them.
CertificatesWhen a site that requires a certificate:
Select one automatically - Firefox will automatically select the relevant certificate and use it to communicate with the server.
Ask me every time - Firefox will prompt you to choose the appropriate certificate before making a connection.