Here are 3 tools that can speed up Firefox response (on Windows), particularly on slower connections.
Firefox normally sends a request to a server and then wait for a response before continuing. Pipelining enables firefox to send multiple requests before any responses are received. This could be helpful when opening multiple tags. To enable, enter about:config in the address bar, double-click and set to true network.http.pipelining and network.http.proxy.pipelining, then double-click network.http.pipelining.maxrequests and set this to a higher value, may be 7 or 8.
Please note that some servers don't support pipelining, and the tweak can actually reduce performance in such sases. Reset network.http.pipelining and network.http.proxy.pipelining to false again if you experience such problems.
Large, complex web pages can take a while to download. Firefox by default will display what it's received so far every 0.12 seconds (the "content notify interval"). While this helps the browser feel snappy, frequent redraws increase the total page load time, so a longer content notify interval will improve performance.
Enter about:config in the browser, then right-click somewhere in the window and select New > Integer. Type content.notify.interval as your preference name, click OK, enter 500000 (five hundred thousand) and click OK. Then right-click again in the window and select New > Boolean. Now create a value called content.notify.ontimer and set it to True.
If no mouse movement or keyboard entry is detected for 0.75 seconds (content switch threshold) then Firefox enters a low frequency interrupt mode, which means its interface becomes less responsive and pages load more quickly. Reducing the content switch threshold therefore can improve performance.
Enter about:config in the browser, then right-click in the window and select New > Integer. Type content.switch.threshold, click OK, enter 250000 (a quarter of a second) and click OK.