Exif Viewer

Simply put, EXIF (short for Exchangeable Image File Format) data is comprised of a wide variety of settings and info regarding the way a particular photo was captured, for instance, ISO and shutter speeds, aperture value, date and time, white balance, camera make and model, lens type, focal length and possibility much more.
Even though knowing all this data might be irrelevant for some professional photographers, for amateurs, it might actually be quite vital, especially for learning-reasons. This said, let's say you stumble upon a picture that captures your attention while you are browsing the Internet and you want to view the EXIF data to gain a little more insight.

Lightweight Firefox add-on that offers a convenient way to view Exif data

Some of the methods that come to mind include, downloading the picture (if that's possible) and uploading it to an online EXIF viewer or saving the file and using a typical photo viewer installed on your computer. By far the simplest method is to view EXIF data with the help of a Firefox add-on, generically named Exif Viewer.
Getting started with the add-on is practically a walk in the park, as you simply need to click the 'Add to Firefox' button from the Firefox official store. A quick restart is required to complete the installation process, mind you.

Works with both remote and local JPEGs

From this point onwards, you can swiftly view EXIF data of most pictures by simply right-clicking on them. Select one of the two available options, 'View Image Exif Data' or ' View Link Exif Data' depending on what you're looking for.
In either case, you are greeted by Exif Viewer's popup main window. The extension sports an intuitive yet quite outdated user interface. The first thing we should point out is the fact that it can display metadata for remote as well as local JPEG images.

Provides you with a decent amount of configuration options

The extension is capable of displaying IFD0, Sub IFD, IFD1, Interop IFD, GPS IFD, IPTC, IPTC Core and Maker Note details. You can handpick which of these options are relevant for you from the View menu. In addition, you are provided with a set of minimalist options, readily available within the main window.
For example, you can ask the extension to display only the basic information, to suppress the image preview, to use tables rather than lists as well as to display the EXIF tag ID.

Exif data, at the tips of your fingers

All in all, Exif Viewer is an efficient Firefox add-on that provides you with a quick way to view the remote or local metadata of JPEG pictures with no more than a few mouse clicks, without having to leave the browser's window and without having to rely on third-party apps to do so.