Firefox Throttle is a small extension that allows you to cap download/upload rates and monitor current bandwidth utilization.
Features - Limit download and upload rates for all open Firefox windows/tabs and downloads - Bursting mode (allow short rate "bursting" after inactivity) - Preset and custom limits - Exclude lists for IP addresses and domains that should not be throttled - Automatically excluded LAN IPs - Traffic stats (for current session and historic since last reset) - Status panel with current bandwidth utilization indicators (or traffic counters) - Quick throttling on/off toggle on status panel