Does it work with the example image provided in the addon's description? (https://pbs.twimg.com/media/DlOC3mOWsAEi1ld.jpg , it should redirect to https://pbs.twimg.com/media/DlOC3mOWsAEi1ld.jpg?name=orig )

To be clear (as stated in the description), it doesn't perform a reverse image search, so it's not necessarily unlikely that the sites you checked didn't have a larger version available that was stored on the site itself. Since I'm not sure which sites you tested it on, I can't really give any specific help regarding the images you tested, sorry!

If however there is a larger version (for example, the link I posted above, an album cover on iTunes, non-original images on Twitter/Instagram/Flickr, etc.) and the script fails to find it, please let me know!

Since (I believe) firefox addons don't allow multiple replies, please feel free to contact me in any of the contact links listed in the addon's description (github, reddit, or discord). I'll try my best to help! :)