Today we have SVGMatrix and CSSMatrix. Both of these have immutable calls: they create a new matrix and return the results in that. This is the norm for DOM classes, but for a Matrix class that can add a lot of overhead, especially when many operations are done at frame rate, as in WebGL.
We should have a mutable Matrix class, which SVGMatrix and CSSMatrix can be derived from.
*** This bug has been marked as a duplicate of bug 50633 ***