MarcZ,

I have avast standard shield set to high and scan everything, i checked and avast does scan my firefox extensions (tested with Firefox 1.0 and Print It 2.1 extension).

If you want to check for yourself, click the avast “A” ball in your taskbar (next to your system clock), then select ‘standard shield’ on the left and click ‘customize’ on the right, then select the ‘Advanced’ tab and check ‘Show detailed infomation on preformed action’, this will show you everything avast is scanning.

–lee