[pwpwp]

This appears to be an artefact of the "async call stacks" feature.

To turn it off in Firefox, go to about:config and set "javascript.options.asyncstack" to false.

In Chrome, in Devtools enter ctrl+shift+p and search for "async stack traces".

[pwpwp]

IOW, there isn't any real stack growth, it just appears that way when running in the devtools with the "async call stacks" feature enabled.