Initially designed as an Firefox add-on, Zotero Version 4.0 now also provides stand-alone support for Chrome, Safari, and Firefox.
To install, access the Zotero download page.
Zotero standalone has to be open in order to save items through the Zotero connector browsers to see Zotero icons in the address bars.
To use the Chrome and Safari connectors without switching to Zotero Standalone, you can actually use the Zotero instance in Firefox as your central repository, and the Safari and Chrome connectors can send citations to it. To do this: