The JSON file extension is used by Mozilla Firefox web browser. Used by Mozilla Firefox from version 3.0 for bookmark backup in JSON format. Firefox version 1.0 - 2.0 stored bookmark backup in HTML file.
JSON is a part of the ECMAScript standard since ECMA has defined in 1999 the eval function that parses the format. It has been popularized with the success of Ajax. The JSON word appears often when one is speaking about Ajax. We know this is another data format, that can replace XML, and this format is supported by a lot of programmers.
You do not need to open the *.json file, you can use Firefox to import the backup file. You can import them using the Library.
Open the Library - Bookmarks → Organize Bookmarks
To import the bookmarks from the json backup, in the Library choose:
Import and Backup → Restore → Choose File
Note that importing a *.json file will replace any existing bookmarks with those in the *.json file.
Firefox automatically creates 5 backup files, and these backups are stored in the bookmarkbackups folder inside the profile folder. On Windows Vista the usual location for the profile folder is:
C:\Users\"Windows login/user name"\AppData\Roaming\Mozilla\Firefox\Profiles\xxxxxxxx.default\
xxxxxxxx is a string of random characters, the second half of that part of the folder name is normally .default but may be something else. The Application Data folder is usually a hidden folder. To show hidden folders, open Windows Explorer and choose:
Organize → Folder and Search Options → Folder Options → View and select Show hidden files and folders