diff --git a/js/src/jit-test/tests/arguments/bug1827073.js b/js/src/jit-test/tests/arguments/bug1827073.js
index a6b1bafa7f7e9..d87ec97b48230 100644
--- a/js/src/jit-test/tests/arguments/bug1827073.js
+++ b/js/src/jit-test/tests/arguments/bug1827073.js
@@ -4,6 +4,8 @@ function f1(a2, a3, a4, a5) {
     f2();
 }
 function f2() {
+    // Recursion depth reduced to allow PBL with debug build (hence larger
+    // frames) to work.
     if (depth++ > 75) {
         return;
     }
diff --git a/js/src/jit-test/tests/asm.js/testJumpRange.js b/js/src/jit-test/tests/asm.js/testJumpRange.js
index 40311e1c7a663..a9ac854d98ad3 100644
--- a/js/src/jit-test/tests/asm.js/testJumpRange.js
+++ b/js/src/jit-test/tests/asm.js/testJumpRange.js
@@ -2,6 +2,8 @@ load(libdir + "asm.js");
 load(libdir + "asserts.js");
 
 var fatFunc = USE_ASM + '\n';
+// Recursion depth reduced to allow PBL with debug build (hence larger
+// frames) to work.
 for (var i = 0; i < 75; i++)
     fatFunc += "function f" + i + "() { return ((f" + (i+1) + "()|0)+1)|0 }\n";
 fatFunc += "function f75() { return 42 }\n";
diff --git a/js/src/jit-test/tests/auto-regress/bug743094.js b/js/src/jit-test/tests/auto-regress/bug743094.js
index 03a1307cd6fd6..982d9d3a87f41 100644
--- a/js/src/jit-test/tests/auto-regress/bug743094.js
+++ b/js/src/jit-test/tests/auto-regress/bug743094.js
@@ -6,6 +6,8 @@ var i = 0;
 
 gczeal(2);
 function test() {
+  // Recursion depth reduced to allow PBL with debug build (hence larger
+  // frames) to work.
   if (i++ > 75)
     return "function";
   var res = typeof (new test("1")) != 'function';
diff --git a/js/src/jit-test/tests/environments/bug1710089.js b/js/src/jit-test/tests/environments/bug1710089.js
index 221d5266c97e5..f7147dc75cc50 100644
--- a/js/src/jit-test/tests/environments/bug1710089.js
+++ b/js/src/jit-test/tests/environments/bug1710089.js
@@ -1,5 +1,7 @@
 // |jit-test| skip-if: getBuildConfiguration()['wasi']
 
+// Recursion depth reduced to allow PBL with debug build (hence larger
+// frames) to work.
 var iters = 75;
 
 // Generate a deeply nested version of:
diff --git a/js/src/jit-test/tests/regexp/bug1697077.js b/js/src/jit-test/tests/regexp/bug1697077.js
index 697a0fedea68f..6ba47881fe20d 100644
--- a/js/src/jit-test/tests/regexp/bug1697077.js
+++ b/js/src/jit-test/tests/regexp/bug1697077.js
@@ -1,4 +1,6 @@
 // |jit-test| skip-if: !('interruptRegexp' in this) || getBuildConfiguration()['pbl']
+// skip testing under PBL because interruption of regex engine here seems to
+// depend on GC behavior and is hard to reproduce reliably.
 var s0 = "A".repeat(10*1024);
 var interrupted = false;
 gczeal(0);