Neither does chromium unfortunately, although Fedora now incorporates the out of tree va-api patches for chromium by default. This is one of the biggest things keeping me on chromium, video acceleration in the browser significantly improves battery life.
There is a package for Arch as well, and it was previously in the default package, but they removed it again temporarily. This is keeping me on Chromium as well, but if it were added to Firefox then I'd reconsider.
