How to stop Firefox spying on you

If you do want to manually manage the settings in Firefox to enhance your privacy, you can do so with the following steps.
First, how to get into Firefox's engine room:
Enter 'about:config' (without the ') in the firefox address bar and press enter.
Press the button 'I’ll be careful, I promise!'
Follow the instructions below…

Secondly, the tweaks:
[1] network.http.sendRefererHeader = 0
(Will disable referrer headers)

[2] network.http.sendSecureXSiteReferrer = false
(Will disable referrer headers between https websites)

[3] privacy.trackingprotection.enabled = true
(Will disable Mozilla’s new built-in tracking protection)

[4] geo.enabled = false
(Will disable geolocation)

[5] browser.safebrowsing.enabled = false
(Will disable Google Safe Browsing and phishing protection. Security risk, but privacy improvement)

[6] browser.safebrowsing.malware.enabled = false
(Will disable Google Safe Browsing malware checks. Security risk, but privacy improvement)

[7] dom.event.clipboardevents.enabled = false
(Will 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)

[8] dom.event.contextmenu.enabled = false
(Will disable website control over rightclick context menu)

[9] geo.wifi.logging.enabled = false
(Will disable firefox logging geolocation requests)

[10] network.cookie.alwaysAcceptSessionCookies = false
(Will disable acceptance of session cookies)

[11] network.cookie.cookieBehavior = 2
(Will 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

[12] network.cookie.lifetimePolicy = 2
(Cookies will be 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

[13] network.dnsCacheEntries = 100
(Number of cached DNS entries. the lower the number, more requests, but less data stored)

[14] network.dnsCacheExpiration = 60
(Time DNS entries are cached in seconds)

[15] places.history.enabled = false
(Will disable recording of visited websites)

[16] browser.formfill.enable = false
(Will disable saving of formdata)

[17] browser.cache.disk.enable = false
(Will disable caching on hardrive)

[18] browser.cache.disk_cache_ssl = false
(Will disable caching for ssl connections)

[19] browser.cache.memory.enable = false
(Will disable caching in memory)

[20] browser.cache.offline.enable = false
(Will disable offline cache)

[21] browser.send_pings = false
(The attribute would be useful for letting websites track visitors’ clicks)

[22] network.dns.disableIPv6 = true
(If your OS or ISP does not support IPv6, there is no reason to have this preference set to false)

[23] network.dns.disablePrefetch = true
(To disable DNS prefetching you will need to add network.dns.disablePrefetch as a new boolean preference and set the value to true)

[24] network.prefetch-next = false
(Link prefetching is when a webpage hints to the browser that certain pages are likely to be visited, so the browser downloads them immediately so they can be displayed immediately when the user requests it. This preference controls whether link prefetching is enabled)

[25] network.websocket.enabled = false
(WebSockets is a technology that makes it possible to open an interactive communication session between the user’s browser and a server)

[26] webgl.disabled = true
(WebGL is a potential security risk. Source here)