You have verified that the Notes Browser Plug-in was installed by looking at Add-ons, Extensions, in the Mozilla Firefox browser version 23.0.1. Notes Browser Plug-in is there and enabled. When you type Notes:Home in the location bar you get a message displaying, "A plugin is needed to display this content."
You type Notes:Home in Internet Explorer, IE, 10. Lotus Notes in the browser Home tab appears.
Mozilla Firefox browser version 23.0.1 is not yet supported at the writing of this article.
A possible workaround is to install an add-on in Firefox that displays IE in a tab.
After installing one of those add-ons,
restarting the browser,
opening a new tab,
switching the tab to IE, and
typing Notes:Home in the location bar, the Notes Browser Plug-in does appear.