--- a/build/moz.configure/rust.configure
+++ b/build/moz.configure/rust.configure
@@ -249,18 +249,16 @@ def rust_target_env_name(triple):
 # We need this to form various Cargo environment variables, as there is no
 # uppercase function in make, and we don't want to shell out just for
 # converting a string to uppercase.
 set_config('RUST_TARGET_ENV_NAME', rust_target_env_name)
 
 # This is used for putting source info into symbol files.
 set_config('RUSTC_COMMIT', depends(rustc_info)(lambda i: i.commit))
 
-set_config('RUSTC_VERSION', depends(rustc_info)(lambda i: str(i.version)))
-
 # Until we remove all the other Rust checks in old-configure.
 add_old_configure_assignment('RUSTC', rustc)
 add_old_configure_assignment('RUST_TARGET', rust_target_triple)
 
 # Rustdoc is required by Rust tests below.
 rustdoc = check_prog('RUSTDOC', add_rustup_path('rustdoc'), allow_missing=True)
 
 # This option is separate from --enable-tests because Rust tests are particularly

--- a/toolkit/library/gtest/rust/Cargo.toml
+++ b/toolkit/library/gtest/rust/Cargo.toml
@@ -8,18 +8,16 @@ description = "Testing code for libgkrus
 [features]
 bindgen = ["gkrust-shared/bindgen"]
 servo = ["gkrust-shared/servo"]
 quantum_render = ["gkrust-shared/quantum_render"]
 cubeb-remoting = ["gkrust-shared/cubeb-remoting"]
 cubeb_pulse_rust = ["gkrust-shared/cubeb_pulse_rust"]
 gecko_debug = ["gkrust-shared/gecko_debug"]
 simd-accel = ["gkrust-shared/simd-accel"]
-oom_with_global_alloc = ["gkrust-shared/oom_with_global_alloc"]
-oom_with_hook = ["gkrust-shared/oom_with_hook"]
 moz_memory = ["gkrust-shared/moz_memory"]
 
 [dependencies]
 mp4parse-gtest = { path = "../../../../dom/media/gtest" }
 nsstring-gtest = { path = "../../../../xpcom/rust/gtest/nsstring" }
 xpcom-gtest = { path = "../../../../xpcom/rust/gtest/xpcom" }
 gkrust-shared = { path = "../../rust/shared" }
 

--- a/toolkit/library/rust/Cargo.toml
+++ b/toolkit/library/rust/Cargo.toml
@@ -8,18 +8,16 @@ description = "Rust code for libxul"
 [features]
 bindgen = ["gkrust-shared/bindgen"]
 servo = ["gkrust-shared/servo"]
 quantum_render = ["gkrust-shared/quantum_render"]
 cubeb-remoting = ["gkrust-shared/cubeb-remoting"]
 cubeb_pulse_rust = ["gkrust-shared/cubeb_pulse_rust"]
 gecko_debug = ["gkrust-shared/gecko_debug"]
 simd-accel = ["gkrust-shared/simd-accel"]
-oom_with_global_alloc = ["gkrust-shared/oom_with_global_alloc"]
-oom_with_hook = ["gkrust-shared/oom_with_hook"]
 moz_memory = ["gkrust-shared/moz_memory"]
 
 [dependencies]
 gkrust-shared = { path = "shared" }
 
 [dev-dependencies]
 stylo_tests = { path = "../../../servo/ports/geckolib/tests/" }
 

--- a/toolkit/library/rust/gkrust-features.mozbuild
+++ b/toolkit/library/rust/gkrust-features.mozbuild
@@ -20,20 +20,8 @@ if CONFIG['MOZ_RUST_SIMD']:
 
 # This feature is only supported on Linux and macOS, and this check needs to
 # match MOZ_CUBEB_REMOTING in CubebUtils.cpp.
 if (CONFIG['OS_ARCH'] == 'Linux' and CONFIG['OS_TARGET'] != 'Android') or CONFIG['OS_ARCH'] == 'Darwin':
     gkrust_features += ['cubeb-remoting']
 
 if CONFIG['MOZ_MEMORY']:
     gkrust_features += ['moz_memory']
-
-# See details in toolkit/library/rust/shared/lib.rs
-# A string test is not the best thing, but it works well enough here.
-if CONFIG['RUSTC_VERSION'] < "1.27":
-    gkrust_features += ['oom_with_global_alloc']
-elif CONFIG['RUSTC_VERSION'] >= "1.28" and CONFIG['RUSTC_VERSION'] < "1.29":
-    gkrust_features += ['oom_with_hook']
-elif CONFIG['MOZ_AUTOMATION']:
-    # We don't want builds on automation to unwittingly stop annotating OOM
-    # crash reports from rust.
-    error('Builds on automation must use a version of rust that supports OOM '
-          'hooking')

--- a/toolkit/library/rust/shared/Cargo.toml
+++ b/toolkit/library/rust/shared/Cargo.toml
@@ -37,18 +37,16 @@ rustc_version = "=0.2.1"
 default = []
 bindgen = ["geckoservo/bindgen"]
 servo = ["geckoservo"]
 quantum_render = ["webrender_bindings"]
 cubeb-remoting = ["cubeb-sys", "audioipc-client", "audioipc-server"]
 cubeb_pulse_rust = ["cubeb-sys", "cubeb-pulse"]
 gecko_debug = ["geckoservo/gecko_debug", "nsstring/gecko_debug"]
 simd-accel = ["encoding_c/simd-accel", "encoding_glue/simd-accel"]
-oom_with_global_alloc = []
-oom_with_hook = []
 moz_memory = ["mp4parse_capi/mp4parse_fallible"]
 
 [lib]
 path = "lib.rs"
 test = false
 doctest = false
 bench = false
 doc = false

--- a/toolkit/library/rust/shared/build.rs
+++ b/toolkit/library/rust/shared/build.rs
@@ -1,8 +1,25 @@
+extern crate rustc_version;
+
+use rustc_version::{version, Version};
+
 fn main() {
+    let ver = version().unwrap();
+    let mut bootstrap = false;
+
+    if ver >= Version::parse("1.24.0").unwrap() && ver < Version::parse("1.27.0").unwrap() {
+        println!("cargo:rustc-cfg=feature=\"oom_with_global_alloc\"");
+        bootstrap = true;
+    } else if ver >= Version::parse("1.28.0-alpha").unwrap() && ver < Version::parse("1.29.0").unwrap() {
+        println!("cargo:rustc-cfg=feature=\"oom_with_hook\"");
+        bootstrap = true;
+    } else if std::env::var("MOZ_AUTOMATION").is_ok() {
+        panic!("Builds on automation must use a version of rust that supports OOM hooking")
+    }
+
     // This is a rather awful thing to do, but we're only doing it on
-    // versions of rustc, >= 1.24 < 1.27, that are not going to change
-    // the unstable APIs we use from under us (1.26 being a beta as of
-    // writing, and close to release).
-    #[cfg(any(feature = "oom_with_global_alloc", feature = "oom_with_hook"))]
-    println!("cargo:rustc-env=RUSTC_BOOTSTRAP=1");
+    // versions of rustc that are not going to change the unstable APIs
+    // we use from under us, all being already released or beta.
+    if bootstrap {
+        println!("cargo:rustc-env=RUSTC_BOOTSTRAP=1");
+    }
 }