I don’t want avast to be on because it interferes with the download speed and some of my other computer operations and software. I’m in process of downloading over 1,000 files totalling over 1 TB from a trusted website, and I don’t want any interference!

If you turn off all the shields, how does avast scan it?
That's essentially my original OP question! I don't know how, but it does... After the file has been downloaded with Firefox, it then says that it's scanning for viruses, then shows a graphic while that scanning process is taking place. It takes at least several seconds, uusually. Some of the files are over 1 GB in size so it takes longer.
If you exclude the website/filetype this is for one particular shield, so will be caught by the File System Shield and scanned, as created.
I made the exclusions in two of the shields, the Web shield and the File System shield. That's the only places to make exceptions that I could find.