If your Firefox toolbar has not been customized to show our Dashlane extension, the latter could be missing from the toolbar although it's properly installed and enabled in the Add-ons section. Our extension should normally appear by default in your Firefox toolbar, however it could indeed be missing if you manually removed it from the toolbar, for instance.
If needed, please follow this little clip from Mozilla to check how to add an extension to your toolbar. Make sure to do that with the Dashlane extension!
If that doesn't help and your extension still doesn't appear in your Firefox toolbar, please refer to this article instead.