GPThemes - ChatGPT Customization is a free Firefox extension designed to personalize the ChatGPT interface. It allows users to adjust chat bubble widths and prompt field sizes, offering full-width options for a more immersive chat experience. Users can also select custom fonts, accent colors, and toggle between modern themes like Light, Dark, and Black (AMOLED). The extension features a clean layout with generous spacing, enhancing readability and flow, complemented by subtle animations that add elegance to the chat interface.

The extension supports various functionalities tailored for GPT-4o and its associated features, although it is not fully compatible with premium models and certain elements. Users can effortlessly switch themes using a floating button, maintaining a visually appealing chat environment. GPThemes is open-source, ensuring accessibility for all users while saving preferences for a consistent experience across different ChatGPT URLs.