Zotero for Firefox lets you capture and organize all your research without ever leaving the browser. Choose Zotero for Firefox if:
Zotero for Firefox runs as a plugin for the Firefox web browser, not as a separate program.
Zotero Standalone runs as a separate application and plugs into your choice of browser. Choose Zotero Standalone if:
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 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.
Note: You can install both Zotero Standalone and Zotero for Firefox and use both on the same computer.
The Zotero download page offers a choice of version depending upon your preferred browser: