Extensions are usually found at Menu -> Add-ons and Themes -> Extensions tab Sometimes they end up in the Customize panel or in the toolbar Overflow Menu. Others, like Dragon NaturallySpeaking, are actually installed as a Plugin Menu -> Add-ons and Themes -> Plugins tab I notice, in your screenshot, a "dead" space on your toolbar which may be the extension that you're looking for but is "blacked out" by your Theme. As a last resort, you can go to Customize Toolbars... and click on the Restore Defaults button. Customize Firefox controls, buttons and toolbars https://support.mozilla.org/en-US/kb/customize-firefox-controls-buttons-and-toolbars

In case you use Private Browsing mode, see: *https://support.mozilla.org/en-US/kb/extensions-private-browsing