This FAQ for the AMO site addresses some topics not currently covered by the Firefox Support website. The Support website includes introductory information about customizing Firefox with add-ons as well as articles on:

Troubleshooting add-on installation, plugins & general issues.
How to uninstall add-ons and troubleshooting uninstallation.
Dealing with problematic add-ons / Gray Bar issue

https://addons.mozilla.org/en-US/firefox/pages/experimentalAddons

Firefox Add-on Questions

What is an Add-on?

Firefox Add-ons let you add features which aren't part of Firefox. Themes change the appearance of Firefox without changing the functionality. Search Plugins and Dictionaries/Language Packs add additional options to Firefox. Extensions add more extensive features to the browser; some add simple toolbars while others can add a wide range of new features.

Are add-ons easy to install?

Yes! Add-ons are very easy to install, typically with one click and a browser restart. They're generally much smaller than a normal application and download very quickly. If you don't like one, they are just as easy to remove or disable.

How do I manage an add-on?

In Firefox, go to "Add-ons" in the Tools menu to manage Themes and Extensions. If your Extension has special options, you can see them in the Extensions section of the Add-ons window. From here, you can also disable and uninstall add-ons. Dictionaries are installed as Extensions Search Plugins can be managed in the Search Bar.

Can add-ons make Firefox slower?

In most cases, add-ons do not cause a perceivable slowdown in Firefox. However, since they are applications, some may affect the performance of Firefox depending on your system configuration. If you suspect that an add-on is affecting the way Firefox runs on your machine, try disabling it.

Why would I disable an add-on?

Disabling an add-on prevents it from loading when you start Firefox, but it doesn't remove the add-on or any of its settings. Enabling the add-on again will bring it back to where it was when you disabled it. For add-ons that you want to turn off without removing, disabling is the way to go.

Add-on Site/AMO

Where can I find new themes for Firefox?

I see several add-ons which provide the same capabilities. How do I decide which one is best?

Here

Update Service

Blocklisting Service

I see a great add-on but it says that it's only compatible with Firefox 2.x. Can I still install it in Firefox 3.x?

How do I backup all of the add-ons and themes that I've installed?

I installed a new theme but would like to revert back to the Firefox default theme. How do I do that?

If I have an issue with an add-on, should I contact Mozilla?

What checks are in place to make sure that add-ons are stable and safe to use?

I want to contact an add-on author but he won't reply?

I've upgraded to Firefox 3.x but my add-on no longer works? Why is that?

I've added an add-on and now Firefox is acting funny? What do I do?

I want to remove an add-on but I don't know where or how to do it?

What is Firefox's Safe Mode feature?

What are experimental add-ons?

Can I submit requests for new add-ons?

I'm looking for an add-on developer to help me on a project. Is there a place I can post a request?

Is there a way to sync the add-ons installed on one computer onto another computer?

How many add-ons can I install?

This FAQ is meant for end users; developer FAQ should go in the
author's section of the site.

What applications and versions are supported?

Please see the complete list here.

How do I delete my add-on?

Due to security concerns, it is not possible to delete an add-on once its GUID has been submitted to AMO. Instead, you can "disable" your add-on which will hide it from searches, display pages, and automatic updates. You can disable your add-on by clicking the Disable button on the Edit Add-on page. You can go back at any time and re-enable your add-on from the same page.

Why aren't add-on updates sent out for sandbox'ed add-ons?

Due to security concerns. Add-ons in the sandbox are unmoderated. If automatic updates were enabled, then this could be used for malicious purposes. Going "public" forces a review by an editor and lessens the chance of a rogue add-on doing damage thru automatic updating.

AMO:FAQ