[orca-list] Performance improvement for web content just landed in master

[Joanmarie Diggs <jdiggs igalia com>]

Hey all.

I just made a change to Orca master which should improve performance in 
web content. Enough of the code was touched that testing would be 
greatly appreciated! The potential risk is that we wind up having stale 
attribute information and need to clear what we've cached more frequently.

Thanks!
--joanie