I would like to have a way to see image size not in pixels but in bytes. I tried Tools > Page Info > Media but I have a table with "Size" option not enabled by default and after I have enabled it it writes me "unknown" size for any image in the page. Solution by extension would be just fine.

  • FWIW, I can just right-click an image, select "Show image info" (or whatever Swedish "Visa bildinfo" is in English) and I am taken directly to the Page Info > Media tab with the image I clicked already selected in the list view at the top. And below this I can immediately see the image's URL, type, size (in bytes), dimensions (in pixels) and ALT text. IIRC, the "Show image info" context menu item was previously available by default, but nowadays is hidden until you change a Firefox setting. Commented Jun 22 at 14:05

2 Answers 2


"Page Info > Media" works for me, but I would suggest the "Developer Tools > Network" view: press F12 to open DevTools; open the 'Network' tab; filter for 'Images'; hit F5 to reload the page.

It will show you both the 'Transferred' size of the response (accounting for HTTP headers and compression) and the real 'Size' of the file.

enter image description here


Basically, there are three ways you can do it:

  1. By using Developer Tools which you access by hitting F12 on your keyboard (or right-clicking and inspecting the element)

  2. By installing the extension for Firefox called "Image Size Info"

  3. By installing "Web Developer" by Chris Pederick. Once the extension is installed, you will see a new toolbar button or menu item. Click on the "Web Developer" extension icon. Navigate to Images > View Image Information.

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