The following has been updated or changed thanks to user feedback during rating:

• Added crosshairs
• Updated some tutorial text to be more clear
• Added a background to,  and increased the size of, end-of-level text
• Fixed inconsistent game name
• Preloaded shaders to avoid bad hitching during gameplay
• Restored missing material in main level

I have since uploaded another version which reworks the settings menu to behave more consistently between browsers and platforms. The settings menu is now accessed via a dedicated button or the T key. 

This updated version is now playable on the main page