Edge Canary limited disk usage capability on YouTube video upload

I poked at this a bit more, and made a little test page to benchmark the file read capabilities:

https://bayden.com/test/diskbenchmark.html

This simple page allows you to pick a local file, then the browser reads it into an arrayBuffer. This eliminates the network from the equation, and while it doesn't eliminate all other variables (memory allocation costs, etc), it does provide a less noisy picture. The page itself calculates the number of bytes read and milliseconds elapsed to provide a more precise measure of disk throughput.

When I use this page on a big file on Windows 10 RS5, I note that almost all of the disk activity is charged to "Antimalware Service Executable" and NOT the browser process; the browser process shows little disk activity at all. 

While the results fluctuate (and this is unsurprising given how disk caches work, etc), I do see significant differences in effective throughput based on browser versions.

I haven't yet tried this on multiple machines.

Edge 18 RS5 (Spartan) -----------------
Read 2,139,348,308 bytes in 4651 ms
459,975,985 bytes/s

Firefox 68 -----------------
Read 2,139,348,308 bytes in 4394 ms
486,879,451 bytes/s

Chrome 73 Stable -----------------
Read 2,139,348,308 bytes in 2004 ms
1,067,539,075 bytes/s

Chrome 75 Canary -----------------
Read 2,139,348,308 bytes in 32868 ms
65,089,092 bytes/s

Edge 75.131 Dev -----------------
Read 2,139,348,308 bytes in 10102 ms
211,774,728 bytes/s

Edge 75.134 Canary -----------------

Trial #1

Read 2,139,348,308 bytes in 24106 ms
88,747,544 bytes/s

Trial #2

Read 2,139,348,308 bytes in 2426 ms
881,841,841.715 bytes/s

Trial #3
Read 2,139,348,308 bytes in 11456 ms
186,744,789.455 bytes/s