The test case has been difficult to reduce. I will add a Pernosco link shortly.

Hit MOZ_CRASH(assertion failed: self.next < self.max_depth_ids) at gfx/wr/webrender/src/gpu_types.rs:52

#0 0x7efe0dedde75 in MOZ_Crash /builds/worker/workspace/obj-build/dist/include/mozilla/Assertions.h:254:3
#1 0x7efe0dedde75 in RustMozCrash src/mozglue/static/rust/wrappers.cpp:17:3
#2 0x7efe0dedde24 in mozglue_static::panic_hook::h6e70bafc479dc06d src/mozglue/static/rust/lib.rs:89:9
#3 0x7efe0dedd74b in core::ops::function::Fn::call::h01fce3a141895069 /builds/worker/fetches/rustc/lib/rustlib/src/rust/library/core/src/ops/function.rs:70:5
#4 0x7efe0eea3ea7 in std::panicking::rust_panic_with_hook::haa1ed36ada4ffb03 /rustc/18bf6b4f01a6feaf7259ba7cdae58031af1b7b39/library/std/src/panicking.rs:573:17
#5 0x7efe0d75feb5 in std::panicking::begin_panic::_$u7b$$u7b$closure$u7d$$u7d$::h766b45a4aba7d061 /builds/worker/fetches/rustc/lib/rustlib/src/rust/library/std/src/panicking.rs:498:9
#6 0x7efe0d75233f in std::sys_common::backtrace::__rust_end_short_backtrace::h1f2702d296cb32df /builds/worker/fetches/rustc/lib/rustlib/src/rust/library/std/src/sys_common/backtrace.rs:153:18
#7 0x7efe0d75fe7e in std::panicking::begin_panic::hac31b679374f2b0d /builds/worker/fetches/rustc/lib/rustlib/src/rust/library/std/src/panicking.rs:497:12
#8 0x7efe0d86e614 in webrender::batch::BatchBuilder::add_prim_to_batch::h00dcbab8c48e0eb9 src/gfx/wr/webrender/src/batch.rs
#9 0x7efe0d864684 in webrender::batch::BatchBuilder::add_pic_to_batch::h51aa06435a0a950d src/gfx/wr/webrender/src/batch.rs:754:17
#10 0x7efe0d8d397c in webrender::frame_builder::FrameBuilder::build_composite_pass::h2897c6b6ac3405ac src/gfx/wr/webrender/src/frame_builder.rs:680:9
#11 0x7efe0d8d397c in webrender::frame_builder::FrameBuilder::build::h555ef9a28b65ec84 src/gfx/wr/webrender/src/frame_builder.rs:605:13
#12 0x7efe0d94ec44 in webrender::render_backend::Document::build_frame::he866ad0ae04ddf8f src/gfx/wr/webrender/src/render_backend.rs:622:25
#13 0x7efe0d95f60f in webrender::render_backend::RenderBackend::update_document::h05e8a09a2cf1ca8c src/gfx/wr/webrender/src/render_backend.rs:1504:41
#14 0x7efe0d9570a6 in webrender::render_backend::RenderBackend::prepare_transactions::he75eea222ccb58fe src/gfx/wr/webrender/src/render_backend.rs:1356:28
#15 0x7efe0d9570a6 in webrender::render_backend::RenderBackend::process_api_msg::h6ce486132a911c58 src/gfx/wr/webrender/src/render_backend.rs:1216:17
#16 0x7efe0d7542b3 in webrender::render_backend::RenderBackend::run::h7f1eb8d6e51dabf6 src/gfx/wr/webrender/src/render_backend.rs:892:21
#17 0x7efe0d7542b3 in webrender::renderer::Renderer::new::_$u7b$$u7b$closure$u7d$$u7d$::h65975432768b2a4e src/gfx/wr/webrender/src/renderer.rs:2780:13
#18 0x7efe0d7542b3 in std::sys_common::backtrace::__rust_begin_short_backtrace::hb1530e75c2be29a6 /builds/worker/fetches/rustc/lib/rustlib/src/rust/library/std/src/sys_common/backtrace.rs:137:18
#19 0x7efe0d77311f in std::thread::Builder::spawn_unchecked::_$u7b$$u7b$closure$u7d$$u7d$::_$u7b$$u7b$closure$u7d$$u7d$::h92c8114983b4f2ab /builds/worker/fetches/rustc/lib/rustlib/src/rust/library/std/src/thread/mod.rs:458:17
#20 0x7efe0d77311f in _$LT$std..panic..AssertUnwindSafe$LT$F$GT$$u20$as$u20$core..ops..function..FnOnce$LT$$LP$$RP$$GT$$GT$::call_once::h7bafcc4640a6035a /builds/worker/fetches/rustc/lib/rustlib/src/rust/library/std/src/panic.rs:308:9
#21 0x7efe0d77311f in std::panicking::try::do_call::h5dcda5a149cd5b3d /builds/worker/fetches/rustc/lib/rustlib/src/rust/library/std/src/panicking.rs:373:40
#22 0x7efe0d77311f in std::panicking::try::heb59f92d561db7cb /builds/worker/fetches/rustc/lib/rustlib/src/rust/library/std/src/panicking.rs:337:19
#23 0x7efe0d77311f in std::panic::catch_unwind::hc3b5fa4bdc42fcfc /builds/worker/fetches/rustc/lib/rustlib/src/rust/library/std/src/panic.rs:379:14
#24 0x7efe0d77311f in std::thread::Builder::spawn_unchecked::_$u7b$$u7b$closure$u7d$$u7d$::h66e72f6a7df3047a /builds/worker/fetches/rustc/lib/rustlib/src/rust/library/std/src/thread/mod.rs:457:30
#25 0x7efe0d77311f in core::ops::function::FnOnce::call_once$u7b$$u7b$vtable.shim$u7d$$u7d$::h3faacda5209feeb3 /builds/worker/fetches/rustc/lib/rustlib/src/rust/library/core/src/ops/function.rs:227:5
#26 0x7efe0eeb3459 in _$LT$alloc..boxed..Box$LT$F$GT$$u20$as$u20$core..ops..function..FnOnce$LT$A$GT$$GT$::call_once::h670c50864ac2cb92 /rustc/18bf6b4f01a6feaf7259ba7cdae58031af1b7b39/library/alloc/src/boxed.rs:1042:9
#27 0x7efe0eeb3459 in _$LT$alloc..boxed..Box$LT$F$GT$$u20$as$u20$core..ops..function..FnOnce$LT$A$GT$$GT$::call_once::h2511952749086d81 /rustc/18bf6b4f01a6feaf7259ba7cdae58031af1b7b39/library/alloc/src/boxed.rs:1042:9
#28 0x7efe0eeb3459 in std::sys::unix::thread::Thread::new::thread_start::h5ad4ddffe24373a8 /rustc/18bf6b4f01a6feaf7259ba7cdae58031af1b7b39/library/std/src/sys/unix/thread.rs:87:17
#29 0x7efe226e56da in start_thread (/lib/x86_64-linux-gnu/libpthread.so.0+0x76da)
#30 0x7efe216c3a3e in clone /build/glibc-2ORdQG/glibc-2.27/misc/../sysdeps/unix/sysv/linux/x86_64/clone.S:95

A Pernosco session is available here: https://pernos.co/debug/ZQ9v_rnZFeE978o18km-4Q/index.html

Bugmon Analysis:
Verified bug as reproducible on mozilla-central 20210225092306-8708c121e21c.
The bug appears to have been introduced in the following build range:

Start: 3c3e1e10767c47f5cd94fa938afd21ecb5037cb2 (20200722110937)
End: 64ec8fabcc2d21a1d3a95a4881134873633f1b50 (20200722115525)
Pushlog: https://hg.mozilla.org/integration/autoland/pushloghtml?fromchange=3c3e1e10767c47f5cd94fa938afd21ecb5037cb2&tochange=64ec8fabcc2d21a1d3a95a4881134873633f1b50

Bugmon Analysis
The bug appears to have been fixed in the following build range:

Start: ceb6a73484eada2cb70ca5255f5c9ce37ed73eae (20210309012723)
End: f329ec36e335a764adde8d7a7fa7a085454c870f (20210309053530)
Pushlog: https://hg.mozilla.org/integration/autoland/pushloghtml?fromchange=ceb6a73484eada2cb70ca5255f5c9ce37ed73eae&tochange=f329ec36e335a764adde8d7a7fa7a085454c870f
Removing bugmon keyword as no further action possible. Please review the bug and re-add the keyword for further analysis.

Setting regressed_by field after analyzing regression range found by bugmon.