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Updating to Firefox 3 from Firefox 2, you may find some of your extensions and add-ons are no longer compatible.*

Here are three ways of solving this problem. They range from a risky and easy solution to a more involved but safer fix. I’ve also included how to rescue Firefox when it won’t start.

* Unless of course the extension author has already updated their add-on, in which case three cheers for them.

Firefox Update Incompatible Add-ons: the challenge

If you’re already using Firefox 2, you’ll start Firefox 3 and get a window like this:

Your favourite add-ons and extensions are incompatible with Firefox 3 and no longer work.

Make a list of the ones that don’t work. Now let’s fix them. Choose from the following three solutions.

1) about:config extensions.checkCompatibility fix

You can configure Firefox to load extensions without checking whether they are compatible.

This is instant, easy, but risky.

Use at your own risk

Now, clearly, Firefox checks add-on compatibility and security for a reason. If you skip these checks by following these instructions:

• You can break your computer 
• Firefox may not start
• Firefox may behave strangely
• Add-ons may not work
• Add-ons may behave strangely
• You can can break your computer

However, if you’re a headstrong young turk, give it a whirl.

How to add the settings

1. Run Firefox
2. Reflect for a moment on the fact You can can break your computer

   (Elevate your right hand slightly and turn your palm outwards to form the Abhaya Mudra otherwise known as the Gesture of Fearlessness. With your left hand, sign a waiver that absolves me of all responsibility.)

3. Using the address bar (you know, where you type www.textgoeshere.org.uk) , go to "about:config".
   You’ll get a warning message:

   

4. Select "I’ll be careful, I promise" to continue.
   You’ll get a large list of configuration settings:
   
5. Right click anywhere in the window and select New > Boolean
6. Enter the preference name extensions.checkCompatibility and set the value to false
7. Make another new boolean pair called extensions.checkUpdateSecurity and set the value to false.
8. Restart Firefox

All extensions and add-ons should be loaded.

2) Nightly Tester Tools extension fix

Install the Nightly Tester Tools add-on. I haven’t tried this, but it is said to possess mysterious unearthly power over other extensions.

Right-click on an incompatible extension and chose "Make compatible" from the menu. Use this power wisely, young Padwan.

3) Get stuck into the code fix

Firefox add-ons have .xpi extensions. In fact, .xpi files are zip archives. When you install an add-on, the .xpi is unzipped into your Firefox profile folder.

• What is a profile and how to find the profile folder

Here’s what you’ll find in inside the extensions folder in your profile:

The names of the folder are not human-friendly, but each folder corresponds to one extension.

Every extension specifies which versions of Firefox are compatible in a file called install.rdf:

You can edit the maxVersion, save, and restart Firefox.

Since you’re there anyway, why not have a dig about in the code and see how the extension is put together. It’s really not that complex.

What to do if Firefox no longer starts

If you’ve tried one of these methods and now find Firefox won’t start anymore:

1. Make sure Firefox is really closed (e.g. check the Task Manager in windows)
2. Move all the incompatible extensions into a temporary folder
3. Restart Firefox to confirm that it works
4. Move one incompatible extensions back into your profile folder
5. Repeat steps 3 and 4, until you’ve sifted out the genuinely incompatible extensions.

You still might get some weird bugs, though. I can’t stress that enough. Fortune favours the brave!