With the Greasemonkey addon you can run lots of useful scripts. I use the script Google Image Ripper, because it's more practical than the default Google Images.
This is a screenshot of the Google Images
And this is a screenshot of the Google Images with the script
If you go to the end of the page and click on "Switch to Basic Version", you see the real dimensions of the images, not the thumbnails
links:
Greasemonkey
https://addons.mozilla.org/en-US/firefox/addon/748/
Google Image Ripper
http://userscripts.org./scripts/show/36918
more scripts
http://userscripts.org./
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The "normal" Google don't show previews it only show the text, but with the Google-img addon you can see the previews
note: You need to change the preferences because the default language is the Polish.
Google-img
https://addons.mozilla.org/en-US/firefox/addon/63751/