Michelle answers:

Probably best to leave it the way it is. The default settings are provided for a reason.

However, if you want to know more about about:config in Firefox, try this page (Firefox 2, but a lot of these are still relevant to Firefox 3):
http://lifehacker.com/software/firefox-2/geek-to-live-top-firefox-2-config-tweaks-209941.php

or see the Mozilla (people who make/distribute Firefox) page:
http://kb.mozillazine.org/Firefox_:_FAQs_:_About:config_Entries

It is possible to partly or completely break Firefox by messing up about:config settings. While tweaking it could be a great way to learn about stuff, if you just want performance enhancements without the risk, you could consider using Firefox extensions which will automatically modify about:config, for instance FasterFox:
https://addons.mozilla.org/en-US/firefox/addon/1269

Michelle answers:

Firefox is a Web browser supported on many operating system (Windows, Mac, Linux). It far more secure than Internet Explorer and Safari because of the constant security updates and add-ons available to it. Another great alternative to Firefox is Opera, it said to be just as secure as Firefox and has a much cleaner look to it. I do not recommend Safari, or Google Chrome; they are not as polished yet.

Firefox –
http://www.mozilla.com/en-US/firefox/
Opera –
http://www.opera.com/

Firefox add-ons – (I recommend Adblock Plus)
https://addons.mozilla.org/en-US/firefox/

Opera’s Widgets –
http://widgets.opera.com/

Michelle answers:

There are two causes to this, one is that firefox itself is damaged and needs to be reinstalled, and the other is that your profile data is damaged.

== FIRST TRY REINSTALLING FIREFOX ==

Open internet explorer and go to www.getfirefox.com and download the latest version of firefox, then install it. If this fixes the problem then you’re done, you dont have to follow the remaining steps.

== IF REINSTALLING FIREFOX DOESNT FIX THE PROBLEM ==

Then it means that your profile data is damaged. You can launch firefox in ‘Safe Mode’ to either diagnose the problem, or back up your bookmarks before moving them to a new profile. Or you can just skip the next step and go onto ‘creating a new profile’

== IF YOU WANT TO BACK UP YOUR BOOKMARKS OR DIAGNOSE THE PROBLEM ==

Read on, otherwise skip to the next step.

Start firefox in safe mode: go into your start menu and search for the program “Mozilla Firefox (Safe Mode)”. Launch it and firefox will start without any addons disabled. You can use Safe Mode to back up your bookmarks (File.. -> Bookmarks -> Show All Bookmarks -> Import and Export -> Backup) and then close out of it and start a new profile where you can later import your bookmarks. You can also use safe-mode to remove any recently installed addons which may have caused a problem.

== DO AWAY WITH THE PROBLEMS BY STARTING FRESH ==

You can start a new firefox profile by right-clicking on the firefox icon and selecting ‘Properties’. There will be an editable text field which is labeled as “Target” and it will say something like this:
“C:Program FilesMozilla Firefoxfirefox.exe”
Add a space at the end, followed by the word -ProfileManager so it looks something like this:
“C:Program FilesMozilla Firefoxfirefox.exe” -ProfileManager

Click on “OK” to close the menu and then doubleclick on the shortcut icon to launch Firefox with the profile manager. You can use this opportunity to create a new profile and launch firefox with it — this will allow you to use Firefox. You can choose to delete your old firefox profile or just leave it as-is.

Michelle answers:

Firefox probably installed in a different folder and you now have both versions but the shortcut hasn’t been updated, but firefox 10 and 11 are really firefox 4