There are countless ways to implement autoplay. You apparently got lucky with one particular toolchain in one situation. Tor Browser is FF based and should not be extended by plugins (as that changes fingerprints), and TB plays whatever junk is on that page.
Have a look at how long Google has been unable to disable autoplay (2009).
The maker of Ungoogled Chromium made an autoplay blocker but it had so many failures he abandoned the project hoping Google would have the resources to tackle the problem.
Get an adblocker? Nothing automatically played with Firefox and uBlock.
There are countless ways to implement autoplay. You apparently got lucky with one particular toolchain in one situation. Tor Browser is FF based and should not be extended by plugins (as that changes fingerprints), and TB plays whatever junk is on that page.
Have a look at how long Google has been unable to disable autoplay (2009).
The maker of Ungoogled Chromium made an autoplay blocker but it had so many failures he abandoned the project hoping Google would have the resources to tackle the problem.