Maybe Fission related. (DOMFissionEnabled=1)

Crash report: https://crash-stats.mozilla.org/report/index/46304a62-1d07-49c6-a05d-1a8d00210603

MOZ_CRASH Reason: ```assertion failed: (left == right)
left: `CoordinateSystemId(2)`,
right: `CoordinateSystemId(0)````

Top 10 frames of crashing thread:

0 xul.dll RustMozCrash mozglue/static/rust/wrappers.cpp:16
1 xul.dll mozglue_static::panic_hook mozglue/static/rust/lib.rs:89
2 xul.dll core::ops::function::Fn::call<fn ../88f19c6dab716c6281af7602e30f413e809c5974/library/core/src/ops/function.rs:227
3 xul.dll std::panicking::rust_panic_with_hook ../88f19c6dab716c6281af7602e30f413e809c5974//library/std/src/panicking.rs:595
4 xul.dll std::panicking::begin_panic_handler::{{closure}} ../88f19c6dab716c6281af7602e30f413e809c5974//library/std/src/panicking.rs:497
5 xul.dll std::sys_common::backtrace::__rust_end_short_backtrace<closure-0, !> ../88f19c6dab716c6281af7602e30f413e809c5974//library/std/src/sys_common/backtrace.rs:141
6 xul.dll std::panicking::begin_panic_handler ../88f19c6dab716c6281af7602e30f413e809c5974//library/std/src/panicking.rs:493
7 xul.dll core::panicking::panic_fmt ../88f19c6dab716c6281af7602e30f413e809c5974//library/core/src/panicking.rs:92
8 xul.dll core::panicking::assert_failed::inner ../88f19c6dab716c6281af7602e30f413e809c5974//library/core/src/panicking.rs:135
9 xul.dll core::panicking::assert_failed<webrender::spatial_tree::CoordinateSystemId, webrender::spatial_tree::CoordinateSystemId> ../88f19c6dab716c6281af7602e30f413e809c5974/library/core/src/panicking.rs:143

There are 12 crashes (from 1 installation) in nightly 91 with buildid 20210603094827. In analyzing the backtrace, the regression may have been introduced by patch [1] to fix bug 1713544.

[1] https://hg.mozilla.org/mozilla-central/rev?node=5452bb0b5363

This will ensure that when we re-land bug #1713544, it contains
a fix for an assertion failure that occurs when two transforms
are complex, but combined result in a 2d transform that we can
handle as a compositor surface.

https://hg.mozilla.org/mozilla-central/rev/14db817c9bf2