diff --git a/toolkit/crashreporter/nsExceptionHandler.cpp b/toolkit/crashreporter/nsExceptionHandler.cpp
--- a/toolkit/crashreporter/nsExceptionHandler.cpp
+++ b/toolkit/crashreporter/nsExceptionHandler.cpp
@@ -885,10 +885,46 @@
   return true;
 }
 
 #endif
 
+void
+WriteEscapedMozCrashReason(PlatformWriter& aWriter)
+{
+  const char *reason;
+  size_t len;
+  char *rust_panic_reason;
+  bool rust_panic = get_rust_panic_reason(&rust_panic_reason, &len);
+
+  if (rust_panic) {
+    reason = rust_panic_reason;
+  } else if (gMozCrashReason != nullptr) {
+    reason = gMozCrashReason;
+    len = strlen(reason);
+  } else {
+    return; // No crash reason, bail out
+  }
+
+  WriteString(aWriter, AnnotationToString(Annotation::MozCrashReason));
+  WriteLiteral(aWriter, "=");
+
+  // The crash reason might be non-null-terminated in the case of a rust panic,
+  // it has also not being escaped so escape it one character at a time and
+  // write out the resulting string.
+  for (size_t i = 0; i < len; i++) {
+    if (reason[i] == '\\') {
+      WriteLiteral(aWriter, "\\\\");
+    } else if (reason[i] == '\n') {
+      WriteLiteral(aWriter, "\\n");
+    } else {
+      aWriter.WriteBuffer(reason + i, 1);
+    }
+  }
+
+  WriteLiteral(aWriter, "\n");
+}
+
 // Callback invoked from breakpad's exception handler, this writes out the
 // last annotations after a crash occurs and launches the crash reporter client.
 //
 // This function is not declared static even though it's not used outside of
 // this file because of an issue in Fennec which prevents breakpad's exception
@@ -1086,22 +1122,12 @@
     }
 #endif
     WriteGlobalMemoryStatus(&apiData, &eventFile);
 #endif // XP_WIN
 
-    char* rust_panic_reason;
-    size_t rust_panic_len;
-    if (get_rust_panic_reason(&rust_panic_reason, &rust_panic_len)) {
-      // rust_panic_reason is not null-terminated.
-      WriteAnnotation(apiData, Annotation::MozCrashReason, rust_panic_reason,
-                      rust_panic_len);
-      WriteAnnotation(eventFile, Annotation::MozCrashReason, rust_panic_reason,
-                      rust_panic_len);
-    } else if (gMozCrashReason) {
-      WriteAnnotation(apiData, Annotation::MozCrashReason, gMozCrashReason);
-      WriteAnnotation(eventFile, Annotation::MozCrashReason, gMozCrashReason);
-    }
+    WriteEscapedMozCrashReason(apiData);
+    WriteEscapedMozCrashReason(eventFile);
 
     if (oomAllocationSizeBuffer[0]) {
       WriteAnnotation(apiData, Annotation::OOMAllocationSize,
                       oomAllocationSizeBuffer);
       WriteAnnotation(eventFile, Annotation::OOMAllocationSize,
@@ -1291,19 +1317,11 @@
   if (oomAllocationSizeBuffer[0]) {
     WriteAnnotation(apiData, Annotation::OOMAllocationSize,
                     oomAllocationSizeBuffer);
   }
 
-  char* rust_panic_reason;
-  size_t rust_panic_len;
-  if (get_rust_panic_reason(&rust_panic_reason, &rust_panic_len)) {
-    // rust_panic_reason is not null-terminated.
-    WriteAnnotation(apiData, Annotation::MozCrashReason, rust_panic_reason,
-                    rust_panic_len);
-  } else if (gMozCrashReason) {
-    WriteAnnotation(apiData, Annotation::MozCrashReason, gMozCrashReason);
-  }
+  WriteEscapedMozCrashReason(apiData);
 
   std::function<void(const char*)> getThreadAnnotationCB =
     [&] (const char * aValue) -> void {
     if (aValue) {
       WriteAnnotation(apiData, Annotation::ThreadIdNameMapping, aValue);
@@ -3054,11 +3072,11 @@
     // There should not be any newlines
     return false;
   }
   char* pos = aData;
   while ((pos = strchr(pos, '\\'))) {
-    if (*(pos + 1) != '\\') {
+    if (*(pos + 1) != '\\' && *(pos + 1) != 'n') {
       return false;
     }
     // Add 2 to account for the second pos
     pos += 2;
   }
diff --git a/toolkit/crashreporter/test/unit/test_crash_rust_panic.js b/toolkit/crashreporter/test/unit/test_crash_rust_panic.js
--- a/toolkit/crashreporter/test/unit/test_crash_rust_panic.js
+++ b/toolkit/crashreporter/test/unit/test_crash_rust_panic.js
@@ -1,11 +1,11 @@
 function run_test() {
   // Try crashing with a Rust panic
   do_crash(function() {
-             Cc["@mozilla.org/xpcom/debug;1"].getService(Ci.nsIDebug2).rustPanic("OH NO");
+             Cc["@mozilla.org/xpcom/debug;1"].getService(Ci.nsIDebug2).rustPanic("OH NO\nOH NOES!");
            },
            function(mdump, extra) {
-             Assert.equal(extra.MozCrashReason, "OH NO");
+             Assert.equal(extra.MozCrashReason, "OH NO\nOH NOES!");
            },
           // process will exit with a zero exit status
           true);
 }
diff --git a/toolkit/crashreporter/test/unit/xpcshell.ini b/toolkit/crashreporter/test/unit/xpcshell.ini
--- a/toolkit/crashreporter/test/unit/xpcshell.ini
+++ b/toolkit/crashreporter/test/unit/xpcshell.ini
@@ -6,10 +6,11 @@
   crasher_subprocess_tail.js
 
 [test_crash_moz_crash.js]
 [test_crash_purevirtual.js]
 [test_crash_rust_panic.js]
+[test_crash_rust_panic_multiline.js]
 [test_crash_after_js_oom_reported.js]
 [test_crash_after_js_oom_recovered.js]
 [test_crash_after_js_oom_reported_2.js]
 [test_crash_after_js_large_allocation_failure.js]
 [test_crash_after_js_large_allocation_failure_reporting.js]
diff --git a/toolkit/crashreporter/test/unit_ipc/test_content_rust_panic.js b/toolkit/crashreporter/test/unit_ipc/test_content_rust_panic.js
--- a/toolkit/crashreporter/test/unit_ipc/test_content_rust_panic.js
+++ b/toolkit/crashreporter/test/unit_ipc/test_content_rust_panic.js
@@ -10,12 +10,12 @@
   // Try crashing with a Rust panic
   do_triggered_content_crash(
     function() {
       Cc["@mozilla.org/xpcom/debug;1"]
         .getService(Ci.nsIDebug2)
-        .rustPanic("OH NO");
+        .rustPanic("OH NO\nOH NOES!");
     },
     function(mdump, extra) {
-      Assert.equal(extra.MozCrashReason, "OH NO");
+      Assert.equal(extra.MozCrashReason, "OH NO\nOH NOES!");
     }
   );
 }
diff --git a/toolkit/crashreporter/test/unit_ipc/xpcshell.ini b/toolkit/crashreporter/test/unit_ipc/xpcshell.ini
--- a/toolkit/crashreporter/test/unit_ipc/xpcshell.ini
+++ b/toolkit/crashreporter/test/unit_ipc/xpcshell.ini
@@ -10,6 +10,7 @@
 [test_content_exception_time_annotation.js]
 [test_content_oom_annotation_windows.js]
 skip-if = os != 'win'
 [test_content_memory_list.js]
 skip-if = os != 'win'
-[test_content_rust_panic.js]
\ No newline at end of file
+[test_content_rust_panic.js]
+[test_content_rust_panic_multiline.js]