6 crashes starting with the latest Nightly (87.0a1 20210204093834). The crashing code is from bug 1690396.

Nical, do you want to aim for a fix in the next hour (to get it into the next Nightly) or should it be backed out (with the next merge)?

Crash report: https://crash-stats.mozilla.org/report/index/3863ea8e-f8c9-48e9-a393-d57790210204

MOZ_CRASH Reason: bug: readback rect outside parent rect clip

Top 10 frames of crashing thread:

0 libxul.so RustMozCrash mozglue/static/rust/wrappers.cpp:17
1 libxul.so mozglue_static::panic_hook mozglue/static/rust/lib.rs:89
2 libxul.so core::ops::function::Fn::call /builds/worker/fetches/rustc/lib/rustlib/src/rust/library/core/src/ops/function.rs:70
3 libxul.so std::panicking::rust_panic_with_hook library/std/src/panicking.rs:597
4 libxul.so std::panicking::begin_panic_handler::{{closure}} library/std/src/panicking.rs:499
5 libxul.so std::sys_common::backtrace::__rust_end_short_backtrace library/std/src/sys_common/backtrace.rs:141
6 libxul.so rust_begin_unwind library/std/src/panicking.rs:495
7 libxul.so core::panicking::panic_fmt library/core/src/panicking.rs:92
8 libxul.so core::option::expect_failed library/core/src/option.rs:1260
9 libxul.so webrender::picture::PicturePrimitive::take_context gfx/wr/webrender/src/picture.rs:5455

Aryx is going to back this out - I'll to to repro and investigate today.

Backed out Bug 1690396 for causing ^ crashes.

backout: https://hg.mozilla.org/mozilla-central/rev/f259675c88bf6bb78eed73238ba942804417c750