To install the Zotero Firefox extension, visit Zotero.org with Firefox and click the red “Download Now” button. Click the “Zotero 3.0 for Firefox” link. If a yellow band appears at the top of the web page with “Firefox prevented this site (www.zotero.org) from asking you to install software on your computer.”, click the “Allow” button. Then click the “Install Now” button in the “Software Installation” pop up window (the button may be greyed out for a few seconds while Firefox downloads Zotero), and restart Firefox after the installation has completed. You should now see the Zotero logo () in the status bar in the right bottom corner of your Firefox browser window.

Video by the Harvard Kennedy School Library

By default Firefox checks periodically for updates of installed extensions, including Zotero. Users can update extensions manually from Firefox's “Add-ons Manager”: “Tools” menu → “Add-ons” → gear icon → “Check for Updates”.

Note that special considerations apply when upgrading from Zotero 1.0 to 2.1.

If you've installed Zotero but the Zotero icon doesn't show up in Firefox, see No Status Bar Icon.

If you get an installation error, try the following steps to install Zotero:

1. Restart Firefox completely and try again.
2. Clear the browser cache and try again.
3. Right-click the “Zotero for Firefox” link and save the Zotero XPI file (e.g. “zotero-2.1.10.xpi”) to your computer. Then drag the XPI file onto a Firefox window to install it.
4. Download the Zotero XPI file from a different browser (e.g., Chrome, Safari, or Internet Explorer) or network—or have someone else do so—and e-mail it to yourself. Then drag the XPI file onto a Firefox window to install it.
5. Restart your computer and try again.
6. Zotero can also be installed from Mozilla's Firefox Add-ons site rather than from zotero.org, but this has a significant disadvantage: because every extension release is reviewed by Mozilla, it can take a while before Zotero updates become available through their site, leaving you behind the latest available version. Even if a problem with your network is preventing the installation, having someone on a different network download the file and send it to you is the preferred solution.

Mozilla also provides documentation for certain errors, such as error -203 and error -228.