From other side, I'm made recently new IPC embedding based on mozilla-central source code. which is actually very nice alternative to MicroB IPC stack and Webkit2 IPC stack.
This IPC embedding is basically mix of Fennec(Chromium IPC approach) but without XUL/XPCOM/Gecko on UI side, and easily embeddable into any toolkit, Qt or GTK.
On N9 I have 60FPS scrolling + ~30% CPU free for simple scrolling zooming operations with Simple QML UI.
I guess if it is compiled on Maemo5 it should be not much slower.
Also Flash works/WebGL/CSS3/3D/ et.c
https://wiki.mozilla.org/Embedding/IPCLiteAPI - here is a bit more info.

Probably someday I'll find time and make build for Maemo5.