A Firefox Guide: Everything you need to know about your fox

1. Which Firefox should I get?

There are a number of Firefox forks other than the ones shown here, but these are probably the most popular.

Firefox (stable)

The most stable, tried, tested, used by millions

Firefox Beta (beta)

Very stable with the latest features

 Aurora (alpha)

"The newest innovations in an experimental environment"

Nightly (pre-alpha)

"These builds are for testing purposes only"

Pale Moon (fork)

Custom-built and optimized for Windows operating systems

Waterfox (fork)

High performance browser specifically for Windows 64-bit systems to enhance speed

2. Fixing Firefox

Disable and/or delete useless plugins:
Disable: Firefox > Add-ons > Plugins > Disable
Delete: Right-click plugin > Show More > "File" (find and delete)

How to restart Firefox in Safe Mode (addons disabled, default theme, default toolbar settings):
Firefox > Help > Restart with Add-ons Disabled

How to reset Firefox to its default state:
Firefox > Help > Troubleshooting Information > Reset Firefox

Create a new profile:
Run: firefox.exe -p
Terminal: firefox -p



3. about:pages

about: Displays your useragent string

about:about Displays all of the about pages

about:buildconfig Displays configure args

about:cache Lists cache entries

about:compartments Shows JS mem

about:config Displays a settings interface

about:crashes Displays all Firefox crashes

about:healthreport Start up times

about:home Displays the home page

about:memory Shows memory

about:permissions Edit site permissions

about:privatebrowsing Private browsing mode

about:support  Prints all add-ons

about:telemetry Performance and usage

about:mozilla Easter egg

about:robots Easter gg

4. Firefox command line (shift+F2)

Save a PNG image of the entire web page:
screenshot --fullpage

Save a PNG image of the visible window only:
screenshot

Restart the browser:
restart

Show all of the available commands: 
help

5. userChrome.css

/* No Firefox Button */
#appmenu-button{display:none !important;}

/* No load progress indicator */
.tab-throbber{display:none !important;}

/* No horizontal scrollbar */
#content browser{margin-right:-14px !important;
overflow-y:scroll; overflow-x:hidden;}

/* No site favicon */
.tab-icon-image{display:none !important;}

/* No "X" button to close tab */
.tab-close-button{display:none !important;}

/* No auto-complete arrow on location bar */
.autocomplete-history-dropmarker{display: none !important;}

/* To make your own userChrome.css tweaks, find elements using the DOM Inspector on "chrome://browser/content/browser.xul" */

6. about:config tweaks

Turn off the new tab page, and makes it about:blank:
browser.newtab.url => about:blank

Turn off Geolocation: 
geo.enabled => false

Turn off file virus-scan after download:
browser.download.manager.scanWhenDone => false

Override the useragent to most common useragent (not needed with Blender/UA Switcher):
New > string: general.useragent.override =>
Mozilla/5.0 (Windows NT 6.1; WOW64; rv:20.0) Gecko/20100101 Firefox/20.0

Force installation of non-updated add-ons:
New > boolean: extensions.checkCompatibility.[version #] => false

Disable prefetching (preloading of pages), which lowers RAM usage:
network.prefetch-next => false 

Override location bar search (pick only one):
keyword.url => "https://duckduckgo.com/html/?q="
keyword.url => "https://startpage.com/do/search?q="

Load plugins when you click them (instead of automatically):
plugins.click_to_play => true

Enable HTTP pipelineing regularly, on SSL pages, and on proxies, respectively:
network.http.pipelining => true
network.http.pipelining.ssl => true
network.http.proxy.pipelining => true

Increase the amount of connections/requests Firefox will make:
network.http.pipelining.maxrequests => 64
network.http.max-connections => 512
network.http.max-persistent-connections-per-server => 32

Speed up the security delay when installing add-ons:
security.dialog_enable_delay => 500

Disable tab animations:
browser.tabs.animate => false

Put cache on RAM:
browser.cache.memory.enable => true
browser.cache.memory.max_entry_size => -1
browser.cache.disk.enable => false
browser.cache.disk.parent_directory => /tmp/firefox 

Reduce page loading delay:
New > integer: nglayout.initialpaint.delay => 0
New > boolean: content.interrupt.parsing => true
New > boolean: content.notify.ontimer => true
New > integer: content.max.tokenizing.time => 100000
New > integer: content.notify.backoffcount => -1
New > integer: content.notify.interval => 100000
New > integer: content.switch.threshold => 2000000
Remove submenu slide delay:
New > integer: ui.submenuDelay => 0

Set a "do-not-track" header to tell sites not to track browsing habits:
privacy.donottrackheader.enabled => true

Disable all Firefox storage settings:
privacy.donottrackheader.enabled => true

Disable Google Blacklists:
browser.safebrowsing.enabled => false
browser.safebrowsing.maleware.enabled => false

Disable prefetching:
network.prefetch-next => true

Disable pings:
browser.send_pings => false
browser.send_pings.require_same_host => true

Disable suggestions on searchbar:
browser.search.suggest.enabled => false

Disable keywords:
keyword.enabled => false

Disable certificates:
browser.ssl_override_behavior => 2

Disable DNS proxy bypass:
network.proxy.socks_remote_dns => true

Disable crash reporting:
In application.ini in the Firefox folder,
[Crash Reporter]Enabled=1 => [Crash Reporter]Enabled=0