HighlightAll is a Firefox extension designed for web development that allows users to highlight all occurrences of a selected word effortlessly. It offers two modes: native mode, which utilizes Firefox's built-in highlighting feature, and custom mode, which employs a third-party library to provide enhanced functionalities. Custom mode enables users to highlight text in multiple colors and shows search markers next to the scrollbar, making it a versatile tool for content analysis and organization.

The extension requires permission to access data on all websites, as it injects a script to perform the highlighting. Importantly, it does not track or read user data, focusing solely on the content of the visited pages. Users can easily remove highlights through the context menu and can customize keyboard shortcuts for enabling or disabling the extension. However, users should be aware of a bug affecting Firefox versions 71 to 74 that may hinder native mode functionality.