Firefox 3.0 is now available, and as many as 1.5 million people have pledged to download it in the first 24 hours. Here's our guide to installing the new browser.

What will happen to my earlier version of Firefox?

The Windows, Linux and Mac OS X versions of Firefox 3.0 all install over your existing version of Firefox and replace it. That means you'll only have one version of the browser on your system after installation, not two. (Unlike the betas, which installed alongside the existing application.)

What will happen to my browsing history and bookmarks?

Firefox 3.0 will grab them straight from your earlier version of Firefox, so you won't need to do anything to retain them.

I use Internet Explorer and want to use the same bookmarks and browsing history in Firefox. What can I do?

It's simple. Choose File/Import, select Microsoft Internet Explorer, then click Next. A page appears that lets you import cookies, bookmarks and browsing history, as well as your internet options. All you have to do is select which you want to import. After that, just click Next, and all the information will be immediately imported.

What will happen to my existing add-ons and extensions?

Here's where your upgrade may run into trouble. Not all existing extensions will work with Firefox 3.0. When you install Firefox 3.0, it will disable all of your extensions until the browser figures out if they're compatible or until a new version of the extension comes out. Every time you launch Firefox 3.0, if it finds an incompatible extension, it checks Addons.mozilla.org to see if there's a newer compatible version. If there is, it offers to update the extension. If there isn't one, Firefox disables the add-on.

However, you don't have to count on the browser doing its work right. It's a good idea to check the website of each extension yourself to see whether a new version has been released. You can also select Tools/Add-ons, select each extension and click Find Updates.

If all that fails and you're feeling brave, you can download the Nightly Tester Tools add-on, which will force Firefox 3.0 to use your existing add-ons, even if newer versions aren't available. Install it, and select Tools/Add-ons to get to the Add-ons screen. It installs a new button on that screen: 'Override all Compatibility'. Click that button, and it will force Firefox to use your existing extensions.

Note that you may see 'Does not provide secure updates' next to some extensions, and so they may not update in this way. In addition, forcing an extension to work in Firefox 3.0 can cause compatibility problems, so use this at your own risk.

HAVE YOUR SAY: visit PC Advisor's Forum to discuss Firefox 3.0

Where is the location of my profile in Firefox 3.0?

Depending on your operating system, your profile will be located in different folders. Here are the folder locations for each operating system:

Windows Vista :Users[UserName]AppDataRoamingMozillaFirefox

Windows 2000, XP and Server 2003:Documents and Settings[UserName]Application DataMozillaFirefox

Mac OS X:~/Library/Application Support/Firefox

Linux:~/.mozilla/firefox

What if I've changed the default location of my profile in Firefox 2.0? Will Firefox 3.0 be able to find it?

Yes, Firefox will detect the profile location and use it, no matter where it is located.

I use multiple profiles. After I install Firefox 3.0, how can I create, delete or use them?

Firefox 3.0 handles multiple profiles the same way that earlier versions of Firefox did, via the Profile Manager.

Windows: Close Firefox, then at a command prompt, type Firefox.exe -profilemanager. A screen will appear that will let you choose which profile to use.

Mac: Assuming that Firefox is installed in the Applications folder, first close Firefox. Then launch Terminal and enter the following command, starting with "/" after the prompt in Terminal: /Applications/firefox.app/Contents/MacOS/firefox -profilemanager. A screen will appear that will let you choose which profile to use. (If you have problems with it, make sure the Firefox application in your Applications folder is specifically named "Firefox.")

Linux: Close Firefox, open the terminal and execute cd, and then execute: ./firefox -profilemanager . A screen will appear that will let you choose which profile to use.

HAVE YOUR SAY: visit PC Advisor's Forum to discuss Firefox 3.0