Browsing Privacy in Mozilla Firefox using about:config

The about:config (Configuration Editor) Page lists Firefox settings known as preferences that are read from the prefs.js and user.js files in the Firefox profile and from application defaults. Many of these preferences are advanced settings that are not present in the Options dialog.

The prefs.js file does not actually contain all of the settings. It only stores changes made to the defaults, after they are written back to disk. prefs.js is a plain-text file that can be edited with a text editor. However, its recommended that you don't edit it directly since you can damage your profile if you make any mistakes.
A user.js file is an alternative method of modifying preferences, recommended for advanced users only. Unless you need a user.js file for a specific purpose you should use about:config instead. The user.js file does not exist by default.

Warning: Changing these advanced settings can sometimes break Firefox or cause strange behavior. You should only do this if you know what you're doing or if you are following trustworthy advice.

How: 

1.     Enter "about:config" in the firefox address bar and press enter.
2.     Press the button "I'll be careful, I promise!"
3.     Follow the instructions below.

Starting Steps :

•     privacy.trackingprotection.enabled = true

        This is Mozilla’s new built in tracking protection.

•     geo.enabled = false

        Disables geolocation.

•     browser.safebrowsing.enabled = false

        Disable Google Safe Browsing and phishing protection. Security risk, but privacy improvement.

•     browser.safebrowsing.malware.enabled = false

        Disable Google Safe Browsing malware checks. Security risk, but privacy improvement.

•     dom.event.clipboardevents.enabled = false

        Disable that websites can get notifications if you copy, paste, or cut something from a web page, and it lets them know which part of the page had been selected.

•     network.cookie.cookieBehavior = 1

        Disable cookies

        0 = accept all cookies by default

        1 = only accept from the originating site (block third party cookies)

        2 = block all cookies by default

•     network.cookie.lifetimePolicy = 2

        cookies are deleted at the end of the session

        0 = Accept cookies normally

        1 = Prompt for each cookie

        2 = Accept for current session only

        3 = Accept for N days

•     browser.cache.offline.enable = false

        Disables offline cache.

•     browser.send_pings = false

        The attribute would be useful for letting websites track visitors’ clicks.

•     webgl.disabled = true

        WebGL is a potential security risk. Source

•     dom.battery.enabled = false

        Website owners can track the battery status of your device. Source

•     browser.sessionstore.max_tabs_undo = 0

        Even with Firefox set to not remember history, your closed tabs are stored temporarily at Menu -> History -> Recently Closed Tabs

Stop Firefox from Scanning your Downloads

 

Whenever you download something off the net, Firefox first downloads it and then shows a “Scanning for viruses” before it makes the file ready to be open. This is often an useless feature, and still ends up not being able to detect the virus on the download. It is better to turn the feature off, rather than to wait for a few valuable seconds before opening your download.

Turning it Off

In Firefox, type about:config as the URL and click on the “I’ll be careful, I promise” button. In the following list that comes, search for browser.download.manager.scanWhenDone. Double click it and set it to false (or right click it and select Toggle). Firefox won’t scan your downloads from now on.

How does Firefox Scan?

Another interesting question would be how Firefox scans your downloads – whether it has its own Anti-Virus definitions like virus programs, or whether it uses an online service to scan the file for viruses.
The answer is neither. Firefox is just a browser and not an AV program. When Firefox tells it is scanning for viruses, what it actually does is call your anti-virus program installed on the computer and make it check for the virus. But since almost all anti viruses have real time protection, the feature is absolutely useless.
In some cases, the “scanning for viruses” also appears on computers without an anti-virus program, in which chase Firefox would be searching for an anti-virus on your computer. So, this makes it a feature thats safe to remove from your Firefox installation.