We describe design decisions informing the development of Gibber, an audiovisual programming environment for the browser. Our design comprises a consistent notation across modalities in addition to high-level abstractions affording intuitive declarations of multimodal mappings, unified timing constructs, and rapid, iterative reinvocations of constructors while preserving the state of audio and visual graphs. We discuss the features of our environment and the abstractions that enable them. We close by describing use cases, including live audiovisual performances and computer science education.