Local Page Editor od LAFL(4xU)R

Local Page Editor is a local-only Firefox extension that lets you customize parts of webpages in your own browser.

You can enable edit mode, click an element on the current page, replace its visible text, input value, or simple HTML, and save the change as a local rule. When you revisit or refresh the same page, the extension automatically reapplies your saved changes.

Common uses include:
=> Personal UI customization
=> Editing labels or values on pages you use often
=> Creating local mock-ups and demos
=> Testing how a webpage would look with different text or numbers
=> Persistently changing table cells or specific page content on your own device

The extension supports exact URL, domain, and path-prefix matching. It also watches for dynamically loaded page content and reapplies matching rules when the page updates.

Important: all changes are local only. This add-on does not modify the real website, server data, or what other users see. It does not collect, transmit, sell, or share user data.