The data that fuels the report can be found by inspecting the
Network traffic using Firefox’s developer tools.
More directly, the description of what data is available can be
found here with the specific data present at
the category/metric subfolder levels, like for
default/cpuSpeed.
It isn’t a spreadsheet, but is instead JSON. The data format is
documented in mozilla/Fx_Usage_Report/'s
DATAFORMAT.md which might help you transform it
for your needs.
I hope this helps!