1)
What is "Acharei Sherirus Libam ha'Ra"?
1.
Malbim: They served idolatry amidst freedom of their hearts and their heart's desire.
2)
Why does it say "Limedum Avosam"?
1.
Radak: Their fathers accustomed them to it 1 . They saw their fathers serve it, and they did the same. 'Avos' are previous generations of Resha'im.