ioquake3

This build needs Quake Live's own game data, which it reads from your local Steam install. How it gets there depends on where Steam put the game.

Quake Live is on another drive

Anywhere outside Program Files — a second drive, or a Steam library you chose yourself.

Read directly from disk. Nothing is copied.

Quake Live is in Program Files

The default Steam install. Browsers refuse to grant folder access there, so the game data has to be dragged in instead.

Drop your steamapps folder here

Copies pak00.pk3 into browser storage — a second copy on your disk, but it only has to be done once.