diff --git a/lib/vernier/output/firefox.rb b/lib/vernier/output/firefox.rb
index 0a7cd09..f1be618 100644
--- a/lib/vernier/output/firefox.rb
+++ b/lib/vernier/output/firefox.rb
@@ -243,8 +243,6 @@ def initialize(ruby_thread_id, profile, categorizer, name:, tid:, samples:, weig
             @strings[filename]
           end
 
-          lines = profile.frame_table.fetch(:line)
-
           func_implementations = filenames.map do |filename|
             # Must match strings in `src/profile-logic/profile-data.js`
             # inside the firefox profiler. See `getFriendlyStackTypeName`
diff --git a/test/output/test_firefox.rb b/test/output/test_firefox.rb
index b8d9d31..e6a5bf6 100644
--- a/test/output/test_firefox.rb
+++ b/test/output/test_firefox.rb
@@ -100,7 +100,7 @@ def test_custom_intervals
 
   def test_thread_names
     orig_name = Thread.current.name
-    th1_loc, th2_loc = nil
+    th1_loc = nil
 
     # Case with just the named, main thread and no location
     result = Vernier.trace do
@@ -135,7 +135,7 @@ def test_thread_names
 
     # Case with named thread and location
     result = Vernier.trace do
-      th2 = Thread.new { th2_loc = file_lineno; sleep 0.01 }
+      th2 = Thread.new { sleep 0.01 }
       th2.name = "named thread"
       th2.join
     end
diff --git a/test/test_rack_middleware.rb b/test/test_rack_middleware.rb
index 864a63e..c5f6acd 100644
--- a/test/test_rack_middleware.rb
+++ b/test/test_rack_middleware.rb
@@ -28,7 +28,7 @@ def test_middleware_enabled
     status, headers, body = response
     assert_equal 200, status
     assert_equal "application/octet-stream", headers["content-type"]
-    assert_match /\Aattachment; filename="/, headers["content-disposition"]
+    assert_match(/\Aattachment; filename="/, headers["content-disposition"])
 
     profile_gzip = body.to_enum.to_a[0]
     profile_json = Zlib.gunzip(profile_gzip)
diff --git a/test/test_retained_memory.rb b/test/test_retained_memory.rb
index 4d2b256..a9a65d3 100644
--- a/test/test_retained_memory.rb
+++ b/test/test_retained_memory.rb
@@ -77,6 +77,7 @@ def test_thread_allocation
     result = Vernier.trace_retained do
       Thread.new { }.join
     end
+    assert_valid_result result
   end
 
   def test_nothing_retained