There are a few tricks to speed up Firefox. Check them out below:

1. Open Firefox.
2. Type about:config in the address bar and press Enter.

HTTP PIPELINING

HTTP is the application-layer protocol that most web pages are transferred with. In HTTP 1.1, multiple requests can be sent before any responses are received. This is known as pipelining. Pipelining reduces page loading times, but not all servers support it.

In the filter bar type network.http.pipelining. Make sure under the value field is says true. If not double-click to set it
Return to the filter bar and type network.http.pipelining.maxrequests. Double-click this option and set its value to 8.
-------------------------------------------------------------------------------------------------
HTTP PROXY

Go to the filter bar and type network.http.proxy.pipelining. Once it opens double-click it to set it to true.
-------------------------------------------------------------------------------------------------
Type network.dns.disableIPv6 in the filter bar and set this option to true by double clicking on it
-------------------------------------------------------------------------------------------------
CONTENT INTERRUPT PARSING

This preference controls whether the application will interrupt parsing a page to respond to UI events. It does not exist by default.
Right-click (Apple users ctrl-click) anywhere in the about:config window and select New and then Boolean from the pop-up menu.


Enter content.interrupt.parsing in the New boolean value pop-up window and click OK.


You will be prompted to choose the value for the new boolean. Select true and click OK.
-------------------------------------------------------------------------------------------------
CONTENT MAX TOKENIZING TIME

Rather than wait until a page has completely downloaded to display it to the user, Mozilla applications will periodically render what has been received to that point. This preference controls the maximum amount of time the application will be unresponsive while rendering pages.
Right-click (Apple users ctrl-click) anywhere in the about:config window and select New and then Integer from the pop-up menu.

Enter content.max.tokenizing.time in the New integer value pop-up window and click OK.

You will be prompted to enter a value. Enter 2250000 and click OK.
-------------------------------------------------------------------------------------------------
CONTENT NOTIFY INTERVAL

This preference specifies the minimum amount of time to wait between reflows. Right-click (Apple users ctrl-click) anywhere in the about:config window and select New and then Integer from the pop-up menu.

Enter content.notify.interval in the New integer value pop-up window and click OK.
You will be prompted to enter a value. Enter 750000 and click OK.
-------------------------------------------------------------------------------------------------
CONTENT NOTIFY ONTIMER

This preference specifies whether to reflow pages at an interval any higher than that specified by content.notify.interval. Right-click (Apple users ctrl-click) anywhere in the about:config window and select New and then Boolean from the pop-up menu
Enter content.notify.ontimer in the New boolean value pop-up window and click OK.
You will be prompted to choose the value for the new boolean. Select true and click OK.
-------------------------------------------------------------------------------------------------
CONTENT NOTIFY BACKOFFCOUNT

This preference controls the maximum number of times the content will do timer-based reflows. After this number has been reached, the page will only reflow once it is finished downloading. Right-click (Apple users ctrl-click) anywhere in the about:config window and select New and then Integer from the pop-up menu.
Enter content.notify.backoffcount in the New integer value pop-up window and click OK.
You will be prompted to enter a value. Enter 5 and click OK.
-------------------------------------------------------------------------------------------------
NGLAYOUT INITIALPAINT DELAY

Mozilla applications render web pages incrementally - they display what's been received of a page before the entire page has been downloaded. Since the start of a web page normally doesn't have much useful information to display, Mozilla applications will wait a short interval before first rendering a page. This preference controls that interval. Right-click (Apple users ctrl-click) anywhere in the about:config window and select New and then Integer from the pop-up menu.
Enter nglayout.initialpaint.delay in the New integer value pop-up window and click OK.
You will be prompted to enter a value. Enter 0 and click OK.
-------------------------------------------------------------------------------------------------
UI SUBMENU DELAY

This preference controls the time a menu takes to open a sub-menu. Right-click (Apple users ctrl-click) anywhere in the about:config window and select New and then Integer from the pop-up menu.
Enter ui.submenuDelay in the New integer value pop-up window and click OK.
You will be prompted to enter a value. Enter 0 and click OK.
-------------------------------------------------------------------------------------------------
PLUGIN EXPOSE FULL PATH

This preference shows full path to plugins in about:plugins. Right-click (Apple users ctrl-click) anywhere in the about:config window and select New and then Boolean from the pop-up menu.
Enter plugin.expose_full_path in the New boolean value pop-up window and click OK.
You will be prompted to choose the value for the new boolean. Select true and click OK.
-------------------------------------------------------------------------------------------------
BROWSER CACHE MEMORY CAPACITY

When a page is loaded, it can be cached so it doesn't need to be rerendered to be redisplayed. This preference controls the maximum amount of memory to use for caching decoded images and chrome (application user interface elements). Right-click (Apple users ctrl-click) anywhere in the about:config window and select New and then Integer from the pop-up menu.
Enter browser.cache.memory.capacity in the New integer value pop-up window and click OK.
You will be prompted to enter a value. Enter 65536 and click OK.

Now u need to Restart Firefox to make affects.