www-client/dooble depends on dev-qt/qtwebkit:4 which is ancient and will never see any security updates.
Since 1.56c has a qt5 USE flag, I'd suggest removing both and just building qt5, as well as removing older versions.
Is there anything stopping us from dropping USE=qt4?
Created attachment 487950 [details, diff]
As of git commits 6787c3c2dbb8cd97b6d03a83fe20f929b6472ef2 and e9f2166473f13a152c6eb1e28743a3be2a213f6e, Qt4 deps have been dropped.