Found Win32-Heri when updating Firefox

My Operating System:  Windows Vista
Product:  AVG ANTIVIRUS FREE  2014
ISSUE:
found virus Win32-Heri  during automatically updating process of  Firefox  on january 28th. 
Reported  Infected files by  AVG  are these:  updater.exe,  mozglue.dll, maintenanceservice.exe, libEGL.dll, breakpadinyector.dll.
Now  I can not  run  Firefox on my pc.   A message is displayed:    "firefox.exe can find component. Error upon beginning because can not find component   mozglue.dll.   Reinstallation might solve the problem."

Hello Sergio,
We understand your concern. We apologize for the inconvenience. Let us inform you that , AVG has launched a new version of AVG free program. We would request you to uninstall AVG old traces using AVG Removal tool and then you can reinstall AVG program on your computer.

Please click on the below link to run AVG remover tool :
http://files-download.avg.com/util/tools/AVG_Remover.exe to completely uninstall your AVG program from your PC.

NOTE: Once the AVG Remover Tool has done with its process. Please go to the C drive and look for a folder named as "AVG Remover" and I request you to delete it manually.

Once you are done with the remover tool please try installing the AVG program by clicking the following link:
http://files-download.avg.com/inst/mp/AVG_Protection_Free_1606.exe

Thank you.