First, be sure that your version of Firefox is the most current version. You may not be able to install the Zotero extension if you do not have the most current version of Firefox.
To get started with Zotero for Firefox, first click the red download button on the Zotero website to download and install the plugin. Be sure to select the Zotero for Firefox extension.
Following the instructions in the video, you see that there are two main parts to Zotero: (1)your online account, stored by Zotero, and accessible from any web browser, and (2) your Zotero extension for Firefox, which, when connected to your Zotero account, allows you to add and organize references in your library.
Zotero Standalone is a good option for users who do not user Firefox as their preferred browser.
To get started with Zotero Standalone, first click the red download button on the Zotero website to download and install the standalone version. Be sure to select Zotero Standalone. You will also need to install a Zotero plug-in for your preferred browser. Zotero offers plug-ins for Firefox, Safari, and Chrome.