login with facebook for another website is blocked

If this is caused by Firefox's Tracking Protection feature, you can turn that feature off for Etsy. While viewing a page on Etsy, click the shield icon at the left end of the address bar. On the drop-down, click the blue slider switch to turn off protection. The page should reload automatically but, if it doesn't reload the page either by clicking the Reload button on the toolbar or by pressing Ctrl+R on the keyboard. Any improvement? If that doesn't work, are you using any Container extensions (such as Facebook Container) that enforce isolation of Meta sites?