image picka for firefox, image downloader (blue icon) for chrome, just make sure to select the bigger resolution as it would most likely give you a selection of every image in the tab. First you click on the image, zoom it in, then click the extensions to select image from.
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eltaco commented
I've used an onlyfans downloader extension for Chrome. You can also press F12 to bring up the elements menu and then use the arrow in the top left of the menu to select the picture. This will give you the direct link for the picture which you can "save as" or open in a new tab.