First, I’m an Avast user and not an Avast Team member.
Given the lack of information it is going to be hard to make any suggestion.
What Operating System ?
What Avast Program are you using and what is the version number ?
Have you recently made any changes to the Avast Settings ?
Are you getting any error messages displayed and if so what ?
Is this happening on all browsers or just one ?
AVAST REPAIR:
- Have you tried an Avast Repair ?
- AvastUI > Menu > Settings > General > Troubleshooting > Repair APP - Restart after completion