An update to Team Fortress 2 has been released. The update will be applied automatically when you restart Team Fortress 2. The major changes include:

• Added the ability to double-click backpack items to use them in Chemistry Sets
  
• Fixed clients not always seeing a warning about using not-tradable items in Chemistry Sets
  
• Fixed not-tradable Strangifiers not applying the not-tradable status to the item they are used on
  
• Fixed the Gunslinger's taunt kill not counting towards taunt kills on a Strange Gunslinger
  
• Removed showing the Marked For Death icon over the head of the local player
  
• Fixed seeing stretched polygons in the HUD 3D Character