Want to store notes you have taken across the Web in your bookmarks? 

Net Notes will allow you to easily store notes on specific sites in your bookmarks.  Once you install Net Notes, you can start taking notes about the active tab you have open.  The Net Notes sidebar can be toggled (shown and hidden) via Firefox view menu, with a toolbar button, or with a customizable keyboard shortcut.  The notes themselves are edited in a simple textbox in your Firefox sidebar.  In the options, you can also set it to open your notes in a bottom bar instead.

When you close the sidebar or open a new window, the content of the notes textbox will automatically be saved for you.  To help you organize, web sites with notes are automatically tagged with a customizable, comma separated list of tags.  Since the notes are stored with your bookmarks, to backup, restore, import and export your notes just backup, restore, import or export your bookmarks.

So if you are searching for a decent note taking add-on for Firefox, Net Notes is well worth checking out over on the Firefox add-ons web site.