Firefox 71 introduces support for CSS subgrid, a feature that greatly enhances web layout design by allowing nested grids to inherit the tracks of their parent grid, facilitating the alignment of elements across varying content lengths. This is particularly useful for aligning elements in common UI components like cards and forms, enabling consistent layout across different browsers through progressive enhancement with @supports and @media queries. The release also brings improvements such as the implementation of the column-span property for multicol layouts, aspect ratio mapping for images to prevent layout jank, and support for the path value in the clip-path property. On the JavaScript side, the update includes support for Promise.allSettled(), which resolves when all promises have been settled, providing developers with more flexibility compared to Promise.all(). These advancements, along with other features, mark Firefox 71 as a significant update for both developers and end-users, aligning with the latest web standards and practices.