To help you speed up or fix issues with your Firefox installation, Firefox offers the Refresh Firefox option, which creates a new Firefox profile. While generally safe, “Refresh Firefox” can interfere with some Zotero functions. Potential issues depend on your version of Zotero.

See Data Missing After Zotero 5 Upgrade.

Note: These directions will not work with current versions of Firefox. Install Install Zotero 5 and follow these instructions.

If you have used “Refresh Firefox” and lost Zotero for Firefox, follow these steps:

1. Re-install Zotero. Don't worry if you find your Zotero library empty at this point.
2. Locate your new Zotero data directory. Keep this directory open, but make sure Zotero (for Zotero Standalone 4.0 or Zotero 5.0) or Firefox (for Zotero 4.0 for Firefox) is closed.
3. In the data directory, you should see a zotero.sqlite with a file size of approximately 1 MB, meaning that it's empty. Rename the data directory folder from “zotero” to “zotero-old”.
4. Locate the “Old Firefox Data” folder on your desktop. This contains your old Firefox data, including your old Zotero data directory. If possible, make a backup of this directory.
5. Locate the “zotero” folder within the “Old Firefox Data” folder. Copy this folder to your current Zotero data directory location.
6. When you now open Zotero, you should find your library restored. You can then delete the “zotero-old” directory.