FlashDroplet per The Iceman

FlashDroplet lets you capture individual frames from any video playing in your browser — with a single click or automatically.
Single capture: Click the extension icon while a video is playing to save the current frame as a PNG file.
Flash scan: Automatically scan through a video to detect and save frames where sudden brightness changes occur — useful for finding flash frames, scene cuts, or highlight moments.
Folder support: Set a custom subfolder name so your captures stay organized by project or session.
No data is collected, no accounts required, and nothing is sent anywhere — all processing happens locally in your browser.