For example Chrome saves here: ~Library/Application Support/Google/Chrome/Default/Current Tabs and Safari here ~/Library/Safari/LastSession.plist. What about Firefox? I found this folder ~/Library/Application Support/Firefox/Profiles/sewzwkcf.default but I cannot spot the right file.
Since version 33, Firefox saves the open session in /sessionstore-backups/recovery.js, inside
your Profile Folder.
Yoric says in this blog post:
• sessionstore-backups/recovery.js
contains the state of Firefox ≤ 15 seconds before the latest shutdown or crash...
...
All these files use the JSON format.
You can see all your open tabs, windows and session info in just a single file, being updated every few seconds.