I bet that once people stop spreading rumors that MMR vaccine contains mercury, the anti-vaccine people will come around. MMR vaccine does NOT contain mercury. (on second thought, they probably won't)
Thimerosal was used to prevent contamination in multi-dose vials (to the best of my knowledge, the only vaccine that currently contains Thimerosal is the ADULT flu vaccine). I have personally given at least hundreds of doses of the MMR vaccine since 1994, and the vaccine has always been in 2 separate single-dose vials (the 1 vial is sterile water, the other is the powdered form of the vaccine). If you look at the prescribing info, you will see that Thimerosal is NOT an ingredient.
In addition, the MMR and mercury "theories" on autism seemed to have merged. From what I gather, though, these are 2 separate theories.
Andrew Wakefield proposes a theory that by giving the measles and mumps vaccine together, there is a risk due to a poorly understood reaction that causes damage to the intestines ("autistic bowel").This was based on a study of 12 autistic children with "severe bowel conditions". That's pretty weak. If the study involved hundreds of autistic children over a period of years, you may be able to have some hope that the theory is correct, but a study of 12?
As for the link between mercury and autism, read this.