Firefox is popular and most successful because of its ability to  customize and add more features to the browser through add-ons.Currently Google Chrome, Safari,IE ,Opera  (Opera 11 alpha)supports extensions. Except for Chrome  and Firefox lot of users doesn’t file type of Opera and Safari extensions, So I compiled a short list of current browsers extensions files formats.

Browser extensions file types

Extension File type
File extension xpi Firefox browser extension
File extension crx Google Chrome extension
File extension   oex Opera browser extension
File extension   safariextz Safari browser extension