The One Button Fields script is designed to be an injected CSS in your site skin. To install it, visit the site skin page and create a new skin (or edit a current skin you have) and then paste the script into the "Extra CSS" section. Press save skin and "use current version." Then clear your browser cache and check someone else's fields to see if it worked as intended.

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It is here: If checking/unchecking this box doesn't do anything, I would suggest removing the script from your qol and/or site skin, clearing your cache. Then re-adding the most recent version in the main post, and clearing your chache again.