FasterFox is a Mozilla firefox add-on which is quite helpful to increase performance of firefox browser. Though it does not increase your Internet speed considerably but I found it quite useful while opening various tabs simultaneously.
According to the official content of Mozilla which is stated below this add-on is more helpful in sending and receiving DNS cache. While watching videos on youtube, this add-on certainly helps in improving the buffering of video content.

Fasterfox allows you to tweak many network and rendering settings such as simultaneous connections, pipelining, cache, DNS cache, and initial paint delay.

Dynamic speed increases can be obtained with the unique prefetching mechanism, which recycles idle bandwidth by silently loading and caching all of the links on the page you are browsing.

Download this add-on at FasterFox(size=116 Kb).