File type: Firefox Bookmarks Backup
The BAK file extension is employed by the Web browser Firefox in providing backups for the user's bookmarks file. Files with this are generated automatically by Firefox in the replacement of bookmarks when the main file gets corrupted.
Every time the Firefox application is installed in the user's computer system, it generates a new instance of the bookmark.html file and names it bookmark.bak.
In cases where the bookmark.html becomes corrupted, the Web browser Firefox retrieves the data contained in the bookmark.bak file right away and renames it so that it becomes the new file bookmark.html.