The memory report was taking using the latest Fx Nightly. The link in the STR is to a PHP profiler front-end. I'll try to leave this box on for a few weeks so you can play with it if needed. It will take roughly 20 minutes to run (assuming the page is focused) and consume roughly 14GB of memory, before failing from what I assume is a process memory limit. Nightly doesn't seem display any error or generate a crash report in this case; progress just stalls, then eventually all the memory is released. Chromium, on the other hand, crashes the tab with an out of memory error.

I don't expect any patches to magically allow the entire file to be processed, but perhaps there is some low hanging fruit to be had here given the sizable difference in memory consumption between Nightly and Chromium. The table below shows the results of running this in Nightly vs a Chromium based browser on an Intel 9700K CPU with 32 GB of memory.

* Memory of process in task manager before failing

STR:

1. Visit https://71.250.207.29/?SPX_KEY=dev&SPX_UI_URI=/
2. Scroll to the bottom of the page and click on the sole entry in the table dated 2020-12-06.

The source repository for the front end can be found at https://github.com/NoiseByNorthwest/php-spx

Looking at the about memory profile, which has 5 GB of Object, 5 GB of ArrayBuffer. I suspect the difference in memory consumption might be related to: https://v8.dev/blog/pointer-compression