Supporters stayed behind after the game to call for Rosenior and chairman Greg Dyke to leave the club.
Rosenior had only taken charge at Griffin Park in the summer following the surprise departure of Martin Allen in a row over transfer funds. They have not managed to win any of their last 16 games.
Youth team coach Scott Fitgerald has been put in temporary charge of the first-team.
"Obviously we don't do these things out of the blue. We had been working on a plan B over the last few weeks in case Leroy had to go," said chairman Dyke.
"There are still a lot of games to go and we are not halfway through the season. If we get the right manager and a bit of luck with injuries we can stay up."