Web browsers have become one of the most commonly used software and are important communication tool to access our data-driven, increasingly visual Internet. Browser graphics speed is essential for many commercial web applications - e-commerce sites, web portals, content management systems (CMS's), therefore web developers should well understand their possibilities. Browsers can be seen as multi-input (HTML-text, images, CSS, Scripts) multi-output (code for processor, graphics card, sound system) translators, but little is known about their 'internal life', especially how they render graphics. Browsers interpreting HTML5 documents have two graphic modes: Retained Mode (images defined in HTML text and animated with CSS) and Immediate Mode (images created on canvas and animated with JavaScript). In order to understand differences of these modes in animation rendering speed were created nine different versions of an animation of Lunar Eclipse which were tested in six major PC and Android mobile phone browsers. Results indicate, that there are no significant differences in major browsers except that IE and Edge (still) lag behind in implementing novel graphics/video formats and that in all tested browsers Retained Mode is at least two times quicker than Immediate Mode.