The capital B makes an 8x difference
Mbps = megabits per second (common for internet bandwidth). MB/s = megabytes per second (common for file transfer). 8 Mbps = 1 MB/s.
Why upload tests and file browsers differ
Broadband providers advertise in Mbps. When uploading a 1 GB file on a 100 Mbps line, the ideal transfer speed is 12.5 MB/s (~80 seconds), before protocol overhead.