Firefox doesn’t support the tab-size attribute, so code in text boxes show 8-space-wide-tabs.
There is an open ticket in Bugzilla tracking this (Bug 737785), but it’s blocked on some implementation changes. TL;DR: Firefox only implements non-prefixed, standardized CSS attributes if it meets the spec, which it currently doesn’t.
Until Firefox implements tab-size, could Discourse add in -moz-tab-size in its style sheets?
Here’s a sample:
def hello_world():
print("Hello, world!")
#2345678
And here’s a screenshot of how it renders on FF nightly 77.0a1 (2020-04-23) (64-bit):
