CardDAV Browser gives you a quick and easy way to connect to a CardDAV server and view vCard details.
Once installed the menu entry will appear under the "Tools" menu. If you are using Firefox and the main menu bar is hidden then the entry can be found under "Developer" in the "burger stack" menu.
You can copy any text or number entry when viewing a vCard by right-clicking on that entry.
Version 6.0: SSL certificate errors are now handled using the built in Mozilla routines.
Version 5.1: Includes the ability to manually specify the username and password or let the Mozilla username and password management system handle authentication automatically.
1) Certain binary vCard fields (eg: Sound) are not displayed.
2) Only 100% CardDAV compliant servers are supported (tested using DAViCal).
3) The only authentication systems available are those built in to Firefox (OAuth is not currently supported).
Unsupported CardDAV Servers:
1) Google (Uses OAuth for authentication).
2) Yahoo (Uses OAuth for authentication).
3) SOGo Open Source Groupware (Is not standards compliant. See here for more information).
4) ownCloud version 9 doesn't work in my testing (Version X does work).