Browsing and editing saved form data in Firefox

The SQLite Manager extension can open the formhistory.sqlite file (as well as any other .sqlite file in a Firefox profile folder) and make it available for adding, editing, and deleting records with the simple GUI.

They're stored in an SQLite database in your profile directory (e.g., C:\Documents and Settings\xxxxx\Application Data\Mozilla\Firefox\Profiles\xxxxx), in a file called formhistory.sqlite.

You can download the SQLite client (executable sqlite) to browse and edit the database.