edit: Thank you for sorting that out. I have done some additional validation and found there was an issue with Firefox 85 and earlier. The required permissions to use some API features changed. I have adapted the addon to deal with this issue. Could you please verify if version 1.2.2 is working again or not?

edit: I am using multiple blockers myself and as far as I know they do not affect the working. Does the addon never function or only on a certain page / image? can you verify this by testing it on images on e.g. wikipedia?

Hi, yes something did change. The extension was updated and additional settings have been added. However this should not have had any effect on your experience. There was a minor issue with the initial update however a fix has been released version 1.2.1 is the most recent.

Please try to reset the "webp image converter" configuration in the addon's options page. This page can be reached by either clicking on the browser button on the top right of your browser window. (The button the webp image converter icon as image). Or by navigating to addon management page (enter about:addons in the adressbar) than click on the three dots next to "webp image converter" entry

In the options navigate to the "generic" and switch to a "advanced" mode than hit reset and confirm.

Reconfigure your favorite settings and try again. If the problems keep persisting please let me know