ok..but why mine blocked firefox ?
If you provide either a screenshot of the blockage or the error message, then perhaps we can hazard a guess as to the 'why'
I too haven't experienced any issue connecting to youtube and I don't have any exclusion set.
What is the exclusion that you have set ?
Where did you set this exclusion ?
That said, I think I recall an issue with URL exclusions in an earlier avast version, I don't know if that has been resolved in this version.