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Zotero is a fantastic tool that collects, manages, and cites research sources. It's free and easy to use.
Each browser has its own version of the Zotero connector, so install the one for the browser you use.
Each browser puts the connector in a slightly different place. See below:
With Chrome, make sure you click the puzzle piece and "pin" the Zotero connector to your browser interface.
** Since the release of Safari 13, the Safari connector has been broken, due to Apple locking down their browser to extensions. If you are a Mac user, please use either the Chrome or Firefox browser and extension instead.