--- a/build/moz.configure/toolchain.configure
+++ b/build/moz.configure/toolchain.configure
@@ -1121,16 +1121,17 @@ js_option('--enable-release',
                'options. This may slow down builds.')
 
 @depends('--enable-release')
 def developer_options(value):
     if not value:
         return True
 
 add_old_configure_assignment('DEVELOPER_OPTIONS', developer_options)
+set_config('DEVELOPER_OPTIONS', developer_options)
 
 # Linker detection
 # ==============================================================
 
 @depends(target)
 def build_not_win_mac(target):
     if target.kernel not in ('Darwin', 'WINNT'):
         return True

--- a/config/rules.mk
+++ b/config/rules.mk
@@ -857,16 +857,26 @@ endif # BUILD_VERBOSE_LOG
 # aren't already present. This essentially restores the default behavior
 # of cargo when running via `mach`.
 ifdef MACH_STDOUT_ISATTY
 ifeq (,$(findstring --color,$(cargo_build_flags)))
 cargo_build_flags += --color=always
 endif
 endif
 
+# These flags are passed via `cargo rustc` and only apply to the final rustc
+# invocation (i.e., only the top-level crate, not its dependencies).
+cargo_rustc_flags = $(CARGO_RUSTCFLAGS)
+ifndef DEVELOPER_OPTIONS
+ifndef MOZ_DEBUG_RUST
+# Enable link-time optimization for release builds.
+cargo_rustc_flags += -C lto
+endif
+endif
+
 # Cargo currently supports only two interesting profiles for building:
 # development and release.  Those map (roughly) to --enable-debug and
 # --disable-debug in Gecko, respectively, but there's another axis that we'd
 # like to support: --{disable,enable}-optimize.  Since that would be four
 # choices, and Cargo only supports two, we choose to enable various
 # optimization levels in our Cargo.toml files all the time, and override the
 # optimization level here, if necessary.  (The Cargo.toml files already
 # specify debug-assertions appropriately for --{disable,enable}-debug.)
@@ -934,17 +944,17 @@ endef
 # This function is intended to be called by:
 #
 #   $(call CARGO_BUILD,EXTRA_ENV_VAR1=X EXTRA_ENV_VAR2=Y ...)
 #
 # but, given the idiosyncracies of make, can also be called without arguments:
 #
 #   $(call CARGO_BUILD)
 define CARGO_BUILD
-$(call RUN_CARGO,build,$(1))
+$(call RUN_CARGO,rustc,$(1))
 endef
 
 define CARGO_CHECK
 $(call RUN_CARGO,check,$(1))
 endef
 
 cargo_linker_env_var := CARGO_TARGET_$(RUST_TARGET_ENV_NAME)_LINKER
 
@@ -979,17 +989,17 @@ endif
 
 # Assume any system libraries rustc links against are already in the target's LIBS.
 #
 # We need to run cargo unconditionally, because cargo is the only thing that
 # has full visibility into how changes in Rust sources might affect the final
 # build.
 force-cargo-library-build:
 	$(REPORT_BUILD)
-	$(call CARGO_BUILD,$(target_cargo_env_vars)) --lib $(cargo_target_flag) $(rust_features_flag)
+	$(call CARGO_BUILD,$(target_cargo_env_vars)) --lib $(cargo_target_flag) $(rust_features_flag) -- $(cargo_rustc_flags)
 
 $(RUST_LIBRARY_FILE): force-cargo-library-build
 
 force-cargo-library-check:
 	$(call CARGO_CHECK,$(target_cargo_env_vars)) --lib $(cargo_target_flag) $(rust_features_flag)
 else
 force-cargo-library-check:
 	@true

--- a/python/mozbuild/mozbuild/frontend/emitter.py
+++ b/python/mozbuild/mozbuild/frontend/emitter.py
@@ -475,17 +475,16 @@ class TreeMetadataEmitter(LoggingMixin):
                         'debug-assertions': True,
                         'codegen-units': 4,
                         'panic': 'abort',
                     }
                 else:
                     expected_profile = {
                         'opt-level': 2,
                         'rpath': False,
-                        'lto': True,
                         'debug-assertions': False,
                         'panic': 'abort',
                     }
 
                 if profile != expected_profile:
                     raise SandboxValidationError(
                         'Cargo profile.%s for %s is incorrect' % (profile_name, libname),
                         context)

--- a/toolkit/library/gtest/rust/Cargo.toml
+++ b/toolkit/library/gtest/rust/Cargo.toml
@@ -37,11 +37,10 @@ rpath = false
 lto = false
 debug-assertions = true
 codegen-units = 4
 panic = "abort"
 
 [profile.release]
 opt-level = 2
 rpath = false
-lto = true
 debug-assertions = false
 panic = "abort"

--- a/toolkit/library/rust/Cargo.toml
+++ b/toolkit/library/rust/Cargo.toml
@@ -35,11 +35,10 @@ rpath = false
 lto = false
 debug-assertions = true
 codegen-units = 4
 panic = "abort"
 
 [profile.release]
 opt-level = 2
 rpath = false
-lto = true
 debug-assertions = false
 panic = "abort"