The Add Subtitles extension for Firefox allows users to seamlessly integrate subtitles into any video element on web pages. This tool is particularly useful for those who require additional accessibility features or wish to enjoy content in different languages. It supports popular subtitle formats such as .srt and WebVTT, providing flexibility in subtitle usage. Users can easily select a video from the extension menu and upload subtitle files from their device or via a URL.

Customization is a key feature, allowing users to modify subtitle appearance by adjusting the color, font, and size. Additionally, the extension includes a delay adjustment feature for perfect synchronization with the video playback. Users can also make videos fullscreen, ensuring that subtitles are displayed appropriately. Note that the extension does not support videos embedded within iframes, requiring a simple workaround to access the desired video.