Avast Password and Roll20

Hi everyone!

I am a Firefox user and a Roll20 player/GM. I have some troubles when opening an official character sheet, it will make Avast Password lag so hard that Firefox would ask me to disable it.
And when I disable Avast Password before joining a game, I have 0 problem to open and edit the character sheet.

Note that the lag does not occur when opening custom sheets, made by ourselves from scratch with HTML+CSS.

Does this come from Avast or Roll20? Am I the only one in this situation?