diff --git a/wasm/app/app.js b/wasm/app/app.js
index 67a172e..c666f30 100644
--- a/wasm/app/app.js
+++ b/wasm/app/app.js
@@ -223,8 +223,14 @@ function runOnTierInWorker(tier, src, onLoading) {
                 // First chunk spawns the in-progress block; subsequent
                 // chunks append to it. User sees displays land
                 // immediately, not just at the end of the run.
+                // Worker splits chunks on \n at the source and sends
+                // each line with an eol flag — re-attach the newline
+                // here so liveBlock.append still walks bytes looking
+                // for charCodeAt 10 and stacks per line. Avoids any
+                // unknown-quantity newline loss between Module.print
+                // and the main thread.
                 if (!liveBlock) liveBlock = startLiveBlock(tier);
-                liveBlock.append(e.data.chunk);
+                liveBlock.append(e.data.chunk + (e.data.eol ? "\n" : ""));
             } else if (e.data.kind === "done") {
                 w.removeEventListener("message", handler);
                 workerState.pending[tier] = null;
diff --git a/wasm/app/worker.mjs b/wasm/app/worker.mjs
index 795f0eb..c729a5c 100644
--- a/wasm/app/worker.mjs
+++ b/wasm/app/worker.mjs
@@ -46,8 +46,40 @@ self.onmessage = async (e) => {
             // blocks the worker, but displays BEFORE/AFTER the bend
             // round-trip surface immediately instead of waiting for
             // the whole eval to finish. Long demos feel alive.
+            //
+            // Defensive newline normalization: the C-tier loader
+            // adds the trailing \n that Emscripten's Module.print
+            // strips, but we kept seeing horizontal output in fox's
+            // Firefox tab as if the \n was lost somewhere on the
+            // wire. To rule out anything between here and the main
+            // thread, split each chunk on \n at the source and post
+            // one message per line — newline preserved as a flag
+            // rather than a byte. The main-thread receiver knows to
+            // re-add the line break.
             (chunk) => {
-                self.postMessage({ kind: "chunk", runId, tier, chunk });
+                if (!chunk) return;
+                let start = 0;
+                for (let i = 0; i < chunk.length; i++) {
+                    if (chunk.charCodeAt(i) === 10) {
+                        self.postMessage({
+                            kind: "chunk",
+                            runId,
+                            tier,
+                            chunk: chunk.slice(start, i),
+                            eol: true,
+                        });
+                        start = i + 1;
+                    }
+                }
+                if (start < chunk.length) {
+                    self.postMessage({
+                        kind: "chunk",
+                        runId,
+                        tier,
+                        chunk: chunk.slice(start),
+                        eol: false,
+                    });
+                }
             },
         );
         self.postMessage({ kind: "done", runId, output });
diff --git a/www/playground/app.js b/www/playground/app.js
index 67a172e..c666f30 100644
--- a/www/playground/app.js
+++ b/www/playground/app.js
@@ -223,8 +223,14 @@ function runOnTierInWorker(tier, src, onLoading) {
                 // First chunk spawns the in-progress block; subsequent
                 // chunks append to it. User sees displays land
                 // immediately, not just at the end of the run.
+                // Worker splits chunks on \n at the source and sends
+                // each line with an eol flag — re-attach the newline
+                // here so liveBlock.append still walks bytes looking
+                // for charCodeAt 10 and stacks per line. Avoids any
+                // unknown-quantity newline loss between Module.print
+                // and the main thread.
                 if (!liveBlock) liveBlock = startLiveBlock(tier);
-                liveBlock.append(e.data.chunk);
+                liveBlock.append(e.data.chunk + (e.data.eol ? "\n" : ""));
             } else if (e.data.kind === "done") {
                 w.removeEventListener("message", handler);
                 workerState.pending[tier] = null;
diff --git a/www/playground/worker.mjs b/www/playground/worker.mjs
index 795f0eb..c729a5c 100644
--- a/www/playground/worker.mjs
+++ b/www/playground/worker.mjs
@@ -46,8 +46,40 @@ self.onmessage = async (e) => {
             // blocks the worker, but displays BEFORE/AFTER the bend
             // round-trip surface immediately instead of waiting for
             // the whole eval to finish. Long demos feel alive.
+            //
+            // Defensive newline normalization: the C-tier loader
+            // adds the trailing \n that Emscripten's Module.print
+            // strips, but we kept seeing horizontal output in fox's
+            // Firefox tab as if the \n was lost somewhere on the
+            // wire. To rule out anything between here and the main
+            // thread, split each chunk on \n at the source and post
+            // one message per line — newline preserved as a flag
+            // rather than a byte. The main-thread receiver knows to
+            // re-add the line break.
             (chunk) => {
-                self.postMessage({ kind: "chunk", runId, tier, chunk });
+                if (!chunk) return;
+                let start = 0;
+                for (let i = 0; i < chunk.length; i++) {
+                    if (chunk.charCodeAt(i) === 10) {
+                        self.postMessage({
+                            kind: "chunk",
+                            runId,
+                            tier,
+                            chunk: chunk.slice(start, i),
+                            eol: true,
+                        });
+                        start = i + 1;
+                    }
+                }
+                if (start < chunk.length) {
+                    self.postMessage({
+                        kind: "chunk",
+                        runId,
+                        tier,
+                        chunk: chunk.slice(start),
+                        eol: false,
+                    });
+                }
             },
         );
         self.postMessage({ kind: "done", runId, output });