diff --git a/js/src/devtools/automation/autospider.py b/js/src/devtools/automation/autospider.py
index 3c067b1cb054..e023b208dfc6 100755
--- a/js/src/devtools/automation/autospider.py
+++ b/js/src/devtools/automation/autospider.py
@@ -224,6 +224,19 @@ elif platform.system() == 'Windows':
 else:
     compiler = 'gcc'
 
+# Need a platform name to use as a key in variant files.
+if args.platform:
+    variant_platform = args.platform.split("-")[0]
+elif platform.system() == 'Windows':
+    variant_platform = 'win64' if word_bits == 64 else 'win32'
+elif platform.system() == 'Linux':
+    variant_platform = 'linux64' if word_bits == 64 else 'linux'
+elif platform.system() == 'Darwin':
+    variant_platform = 'macosx64'
+else:
+    variant_platform = 'other'
+
+
 info("using compiler '{}'".format(compiler))
 
 cxx = {'clang': 'clang++', 'gcc': 'g++', 'cl': 'cl'}.get(compiler)
@@ -294,6 +307,12 @@ else:
 if platform.system() == 'Linux' and AUTOMATION:
     CONFIGURE_ARGS = '--enable-stdcxx-compat --disable-gold ' + CONFIGURE_ARGS
 
+# Override environment variant settings conditionally.
+CONFIGURE_ARGS = "{} {}".format(
+    variant.get('conditional-configure-args', {}).get(variant_platform, ''),
+    CONFIGURE_ARGS
+)
+
 # Timeouts.
 ACTIVE_PROCESSES = set()
 
@@ -448,18 +467,6 @@ def normalize_tests(tests):
     return tests
 
 
-# Need a platform name to use as a key in variant files.
-if args.platform:
-    variant_platform = args.platform.split("-")[0]
-elif platform.system() == 'Windows':
-    variant_platform = 'win64' if word_bits == 64 else 'win32'
-elif platform.system() == 'Linux':
-    variant_platform = 'linux64' if word_bits == 64 else 'linux'
-elif platform.system() == 'Darwin':
-    variant_platform = 'macosx64'
-else:
-    variant_platform = 'other'
-
 # Override environment variant settings conditionally.
 for k, v in variant.get('conditional-env', {}).get(variant_platform, {}).items():
     env[k] = v.format(**REPLACEMENTS)
diff --git a/js/src/devtools/automation/variants/plaindebug b/js/src/devtools/automation/variants/plaindebug
index 31778fcedf97..b88f3656d5fe 100644
--- a/js/src/devtools/automation/variants/plaindebug
+++ b/js/src/devtools/automation/variants/plaindebug
@@ -1,6 +1,7 @@
 {
     "configure-args": "--enable-rust-simd",
     "debug": true,
+    "compiler": "clang",
     "env": {
         "JSTESTS_EXTRA_ARGS": "--jitflags=debug"
     },
@@ -8,5 +9,8 @@
         "linux64": {
             "JITTEST_EXTRA_ARGS": "--run-binast"
         }
+    },
+    "conditional-configure-args": {
+        "linux64": "--enable-clang-plugin"
     }
 }