It doesn't work for Duckduckgo but I added stars just for existing. F**ck the cancer that is pinterest.

Had been working perfectly until I needed to do a full reinstall of windows 10. Now, for some reason, -pinterest is no longer added when doing image searches. Hope a solution is available.

Uninstalled and reinstalled. Cleared cache. Closed Firefox and reopened. Still not adding -site:pinterest.* to image searches. As mentioned, it worked perfectly before I reinstalled both Windows 10 and Firefox. Chrome is working fine again though.