> the only guy who still developes a PPC compatible browser version for PPC Macs

There's more than WebKit:

http://www.tenfourfox.com

> using javascript engine of webkit of 2 or 3 releases ago

Yes, see Fab's latest MorphZone posting:

"[...] it would make sense to update to the latest branch Tobias Netzel uses (r600.8 branch). If i haven't done that yet, it's merely a matter of time, but it wouldn't be very difficult."
https://morph.zone/modules/newbb_plus/viewtopic.php?topic_id=11347&forum=9&start=17