JSON (JavaScript Object Notation) is a light-weight data exchange format based on subset of JavaScript, whenever you encounter JSON document via a URL, Firefox asks you to download that file, but XML file will be displayed correctly with formatted result with collapsible sections. JSONView is an extension available for both Firefox and Chrome lets you view JSON documents in the browsers without the need to download JSON files to your computers.

json file displayed in Firefox with JSONView

Case where you need to view JSON file in Firefox [DIY]

If you plan to reinstall Windows or another Operating System you’re on, you can backup all bookmarks saved in Firefox to a single JSON file from Bookmarks Manager in Firefox (use Ctrl +Shift +B), you can restore that file to restore your bookmarks later if you want.

After installing this extension, whenever you came across a JSON file in a page, this extension automatically displays its contents. Visit this JSON example link to test whether JSONView is working correctly or not.

Download JSONView