Leg extensions? Nah, just squat , as much, as deep and as upright as possible. Front squats are supposedly more quad-dominant. Same for high-bar vs low bar for back squats.
Still, that 135 is weird, it is too low for someone who was in the 300 area on back squats. Maybe it's another issue? e.g. you have to hold the bar with your wrists at the bottom so that's the limiting factor?
Anyway, keep front squatting as you are since you like them, but i think it would be a good idea to alternate them with back squats, like day 1 front - day 2 back.