«Bookmarklet – a small software application stored as a bookmark in a web browser, which typically allows a user to interact with the currently loaded web page in some way.»
Postcard Image Address – get URL (direct web address) for the image of a registered postcard
UPDATED 2017-02-24: Updated due to changes on Postcrossing website
How to use it (video)
Traveling Cards – show images of traveling postcards. Also works for Sent and Received postcards pages
UPDATED 2019-09-19: Works again (adjusted to Postcrossing site change)
How to use it (video)
Random Postcard from Gallery – Show random postcard from Postcrossing Gallery
UPDATED 2017-02-24: Updated due to changes on Postcrossing website
How to use it (video)
Useful information: How enable bookmarks/favorites bar in Google Chrome / Firefox / Internet Explorer / Safari