Zotero Standalone (unlike Zotero for Firefox) runs as a separate program instead of part of your web browser.
It works with Firefox, Chrome and Safari.
Download [link here] and install Zotero Standalone just as you would any other program. You will also need to install the Connectors to allow your browser to save items to your Zotero library.
You can install both Zotero Standalone and Zotero for Firefox and use both on the same computer.
Choose Zotero Standalone if:
Connectors allow your web browser to save citations to your Zotero library.
Each browser has its own version of the Zotero connector, so if you use both Chrome and Safari you'll need to install both.
Firefox does not require a connector to work with Zotero; it's built into Zotero for Firefox.
Word processor plugins allow you to insert citations and bibliographies directly into your documents. Installing them is optional but highly recommended.