Tab2JSON by Simon L Schlee

You can click the tool button to close the current tab and store it as a JSON file.

There are some additional keyboard shortcuts (keys can be changed via the addon preferences):
save current tab without closing it: Ctrl+Shift+Insert
save current tab and close it: Ctrl+Shift+Down
select next tab: Ctrl+Shift+Right
select previous tab: Ctrl+Shift+Left
closes the current tab (without saving): Ctrl+Shift+Up
save and close all tabs of current window: Alt+Shift+P

Currently this tool is mainly for users, who are programmers who like to write their own scripts to categorize and manage their tabs on their own computer. The JSON file contains the following keys: hostname, url, title, favicon, preview and date. The favicon and preview are only sometimes available and stored as data-urls-string or false.