Firefox Throttle is a small plug-in for your favourite Web Browser, that allows you to cap download/upload rates and monitor current bandwidth utilization.
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
English and Russian User Interface
By Web Masters – to monitor real page weights, page load times at different connections speeds, etc.
By small offices with simple network configuration/router – to limit/prevent shared internet connection bandwidth hogging by some individuals
Download Firefox Throttle from here