Give the game a window of its own
Close unused tabs before you start. Each one holds memory, and heavy tabs such as video or spreadsheets compete directly with the game for the same resources.
Confirm hardware acceleration is switched on
In your browser's settings, make sure graphics acceleration is enabled and that your graphics driver is current. This single setting explains a large share of stutter reports.
Turn the in-game settings down first
Shadows, particle effects and resolution scaling cost the most. Lower those before touching anything else, and expect an immediate difference on laptops.
Watch heat and power settings
A laptop on battery saver will throttle within minutes. Plug in, keep the vents clear, and set the power profile to balanced or better during longer sessions.