The Zotero Connector places a save icon — representing the content it recognized on the page you're viewing (book, journal article, webpage) — to the right of the address bar in your browser toolbar:
If you don't see it, first make sure you've installed the Zotero Connector for your browser from the download page and that it shows up as enabled in the browser's Extensions pane. If you're having trouble installing it, make sure you're running a compatible browser version.
If you still can't find it, try the steps below for your browser.
If the button doesn't appear to the right of the address bar, it may also appear in the toolbar overflow panel (referred to as the “Chrome menu” and opened via the three-dots button to the right of the other toolbar buttons). If you find the button in the overflow panel, right-click on it and choose “Keep in Toolbar” to ensure that it stays visible.
If the button doesn't appear to the right of the address bar, it may also appear in the toolbar overflow panel (opened via a “»” button to the right of your other toolbar buttons) or the menu panel (opened via the “Open menu” button with three horizontal lines at the right edge of the toolbar).
If the Zotero Connector is listed as installed but you don't see the save button in the three places listed above, right-click on the toolbar and choose “Customize…”, and then look for the Zotero button in the icon palette. If you see it, drag the button to the toolbar or, if you only use Zotero infrequently and want to save space, the menu panel.
Note that Zotero no longer places a “Z” icon in your Firefox toolbar to open the Zotero pane. See A Unified Zotero Experience for more information.
If you've tried all these steps and are still having trouble, you may have a corrupted Firefox profile. Try creating a new Firefox profile and try installing the Zotero Connector into that profile.