It's a new security feature in Firefox 153, you now need to give file URL access to the extension to continue searching with local images opened in a tab.

Please go to about:addons, click on Search by Image to open the extension's details and visit the "Permissions and data" tab to find the optional permission. The relevant permission is "Access local files on your computer", which is poorly named in my opinion, and will surely confuse and alarm users.

The same permission is named "Allow access to file URLs" in Chrome, which is much less vague and alarming.

https://blog.mozilla.org/addons/2026/07/23/firefox-153-webextensions-api-updates/