YouTube Thumbnail Tester — version 0.4.2. Effective October 15, 2026.

The extension stores your latest thumbnail image, video title, channel name, and optional channel image in Firefox's extension-local storage on your device. Selected images are read locally. The draft is replaced as you edit it and remains after the tester closes or Firefox restarts. The selected video and applied preview state are not saved across sessions. Drafts are not stored using Firefox Sync by this extension.

The developer operates no backend for this extension and receives no drafts, browsing history, analytics, telemetry, or error reports from it. The extension contains no network request code or remote code loading. Clicking its toolbar button may open the YouTube homepage, which makes normal website requests.

The editor and preview are inserted into YouTube's document. Applied thumbnail, title, and channel changes are visible within that page, and page scripts may be able to inspect inserted content, including the editor's open shadow DOM. This is a visual preview tool, not a private vault for confidential drafts. The extension does not upload or publish drafts to your YouTube channel. YouTube's own data processing is governed by its privacy practices.

Private windows are not supported. The extension requests access only to www.youtube.com and activates the tester after a toolbar click. It uses local storage to remember drafts and scripting access to display the tester.

To remove saved draft data, uninstall the extension through Firefox's Add-ons Manager. Closing the tester or refreshing the page restores the page appearance but does not delete the saved draft. Firefox may retain data separately in backups you create or control.

For questions, use https://github.com/Ramanandp/YT-Thumbnail-Tester/issues. Issues are public; do not include private drafts or other sensitive information.