diff --git a/pyproject.toml b/pyproject.toml
index 6a38c8c..5166cb3 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -4,7 +4,7 @@ build-backend = "hatchling.build"
 
 [project]
 name = "invisible-playwright"
-version = "0.3.0"
+version = "0.3.1"
 description = "Playwright wrapper for a patched Firefox with deterministic stealth profile."
 readme = "README.md"
 requires-python = ">=3.11"
@@ -24,11 +24,14 @@ dependencies = [
     # in invisible-core since the 2026-07-03 split; it pulls platformdirs/requests/
     # maxminddb/tzdata/tqdm/pywin32 transitively. The wrapper only adds Playwright.
     "invisible-core @ git+https://github.com/feder-cr/invisible_core.git",
-    "playwright>=1.40,<1.61",
+    # Pinned to the Juggler client we actually test against (scripts/playwright_pin.txt,
+    # 1.55.x). Playwright 1.61 added an isMobile field to Browser.setDefaultViewport that
+    # the FF150 Juggler does not accept, which breaks the session (issue #48).
+    "playwright>=1.55,<1.56",
 ]
 
 [project.optional-dependencies]
-dev = ["pytest>=7", "pytest-mock>=3", "responses>=0.24", "build>=1", "pytest-rerunfailures>=14", "playwright>=1.40,<1.61"]
+dev = ["pytest>=7", "pytest-mock>=3", "responses>=0.24", "build>=1", "pytest-rerunfailures>=14", "playwright>=1.55,<1.56"]
 
 [tool.pytest.ini_options]
 markers = [