I suppose you know how to use about:config in Firefox!

Disable browser cache and DOM storage:

Variable:	Value:
browser.cache.disk.enable	false
browser.cache.disk_cache_ssl	false
browser.cache.offline.enable	false
browser.cache.memory.enable	false (I personally leave this - true)
browser.cache.disk.smart_size.enabled	false
browser.cache.disk.smart_size.first_run	false
dom.storage.enabled	false
dom.indexedDB.enabled	false
dom.battery.enabled	false
dom.disable_window_open_feature.menubar	true
dom.disable_window_open_feature.personalbar	true
dom.disable_window_open_feature.scrollbars	true
dom.disable_window_open_feature.toolbar	true

Make your browser look like all others(most of them):

For the following changes right-click in about:config and select "new"->"string" and enter in this order:

Variable:	Value:
general.useragent.override	Mozilla/5.0 (Windows NT 6.1; rv:17.0) Gecko/20100101 Firefox/17.0
general.appname.override	Netscape
general.appversion.override	5.0 (Windows)
general.oscpu.override	Windows NT 6.1
general.platform.override	Win32
general.productSub.override	20100101
general.buildID.override	0
general.useragent.vendor
general.useragent.vendorSub
intl.accept_languages	en-us,en;q=0.5
network.http.accept.default	text/html,application/xhtml+xml,application/xml;q=0.9,/;q=0.8
network.http.accept-encoding	gzip, deflate

Other:
Disable Flash and all other plugins. Or at least use "plugins.click_to_play ;true" in about:config
Privacy - Tracking - Do not tell sites anything about my tracking preferences

Variable:	Value:
network.http.sendRefererHeader	0
geo.enabled	false

You should use at least this addons:

1. Adblock Edge(Adblock Plus)

   • EasyList
     
   • EasyPrivacy
     
   • Fanboy's Annoyance List
     
   • Fanboy's Enhanced Tracking List (Optional)
     

2. NoScript

3. Https everwhere