The home side were a man down from as early as the sixth minute when full-back Robbie Ryan was sent off for handling Andy Scott's shot on the goal-line.
Former Rovers player Matthew Lockwood confidently beat Kevin Miller with a side footed spot kick and the visitors looked to be taking early command.
But Rovers refused to lie down and five minutes after the break a linesman spotted Scott handle a right-wing cross from Junior Agogo.
Forrester stepped up to lash the ball into the roof of the net and from then on either side might have snatched all three points in an exciting second half.
Miller twice did well to deny lively striker Lee Barnard, while at the other end Dave Savage had a 79th minute shot deflected when it looked goalbound.
Savage had been booked for diving on 16 minutes as he went head first in the area claiming a penalty. The fall looked a delayed reaction and referee Clive Penton was not fooled.
Orient created the better chances and were unlucky on 42 minutes when Brian Saah's firm shot was spectacularly cleared off the line by Stuart Campbell.
Agogo was left as a lone raider for much of the time by Rovers after Ryan's sending-off, but still carried the pace and strength to keep Orient defenders on their toes.
Orient will be disappointed not to have made the advantage tell and manager Martin Ling will rue the lack of a killer punch in front of goal.
For Rovers in the circumstances it was a point well won and Ian Atkins will be pleased with the way his side reorganised following their early setback.