Firefox about:config edits

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8-Dec-17: Added a section on WebRTC.
Firefox updates can sometimes restore default
about:config settings. We need to keep an eye
on them, particularly the likes of turning 
off DOM storage. The script that is linked to a
little down the page is one way of defending
against loosing important settings. You can edit
this script to suit yourself too.

The about:config Firefox & Pale Moon Preferences Page

The top three or so about:config preferences topics here are duplicated in this wiki page: [1] A page dedicated to Firefox (& now also Pale Moon) security, which I strongly recommend you read, whether you use either of those browsers or not.

Editing the Firefox/Pale Moon about:config Preferences

About-config firefox.png
  • Some background on the about:config Preferences page as shown to the left:

A user.js script that you should know about

Keep an eye on this section, as there is some very
valuable information coming here soon... ;)
I've not checked whether such a script will work with
Pale Moon? Someone may give it a try & let me know?

Read about the script here: [2]

Be advised that using this script will overwrite any
& all modifications that you have made to Firefox via
about:config edits - every time you start Firefox... 
So you can NOT loose your settings to a Firefox update.

One way to use the information in the script is to look at it here: [3] & then manually edit your about:config with any & all options that you choose to use, using copy/paste to find & change where applicable.

Though, I think that the best way to use this script is to edit it & add those things that you would like included & remove any that you have no need for (or that have been upgraded into oblivion my mozilla).

Spending the time to edit this script (which is not hard to do after looking at its format), to suit yourself, will ultimately save you a lot of time in the future. As you will be able to copy it from your backup into any Firefox install that comes.

If you need to edit the about:config, it is easier to edit the user.js script, making any aditions/removals & then just restart Firefox & your about:config will be edited automatically & loaded with Firefox each time it starts (have I mentioned that already?).

This is very useful information, thanks to salome for bringing it to our attention in the forum (long ago now).

WebRTC - Turn it OFF

This is from the page:

Mozilla Firefox: Type about:config in the address bar. Scroll down (or search for) to media.peerconnection.enabled, double click to set it to false.

If you don't know about WebRTC a quick search on the web will expose its dangers, particularly to those that use a VPN.

Turn off DOM Storage

DOM storage has become a much bigger threat to our privacy than the dreaded cookies were. Unfortunately this technology is certainly set to leave cookies in the dust, so changing the default value of this configuration to false is strongly recommended for security reasons. However, please note that it may cause a few web sites not to work properly at the same time.

Works with Pale Moon.

about:config Name:

Default value: true

Modified value: false

The following is quoted from [4] though they have moved it for whatever reason, the above links to their main page on DOM:

HTML5 web storage, a better local storage than cookies. What is HTML5 Web Storage?

With HTML5, web pages can store data locally within the user's browser.

Earlier, this was done with cookies. However, Web Storage is more secure and faster. The data is not included with every server request, but used ONLY when asked for. It is also possible to store large amounts of data, without affecting the website's performance.

The data is stored in key/value pairs, and a web page can only access data stored by itself.

Referrer Control

Works with Pale Moon.

about:config Name: network.http.sendRefererHeader

Default Value: 2

Modified Value: 0

By setting network.http.sendRefererHeader in about:config to 0, whenever you visit a link from one site, the destination site doesn't know the original site you were referred from.

This in effect makes the Firefox add-on RefControl (& others) redundant.

From the Knowledgebase:
network. http. sendRefererHeader	Integer
Determines when to send the Referer HTTP header.
0: Never send the referring URL
1: Send only on clicked links
2 (default): Send for links and image

If you find that you can't get into your online banking (or other) site, it can be due to you having set the integer to 0. You would then be best off using the integer value of 1. & Under such circumstances use the likes of RefControl as you can use whatever options you choose for your normal surfing & then choose a specific option that works with specific troublesome sites.

I am very rarely blocked from a site (for whatever reason) & under such circumstances I don't want to use the site anyway!

Prefetch Control

Works with Pale Moon.

about:config Name: network.prefetch-next

Default Value: true

Modified Value: false

By setting network.prefetch-next to false, we are controlling the following:

Link prefetching, is when a web page 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 request

How to Quash both Firefox & Pale Moon's Silent Requests

Works with Pale Moon.

about:config Name: network.http.speculative-parallel-limit

Default Value: 6

Modified Value: 0

By setting network.http.speculative-parallel-limit to 0, we are controlling the following:

Unlike older versions of Firefox, more recent versions will make a request to a destination server just by hovering over a link. No CSS, no JavaScript, no prefetch required.

For more information on this topic see the following slashdot page: [5]

User Agent Strings

Pale Moon has its own custom settings, which are used
to make Pale Moon as compatible as possible with the
majority of web sites/pages.
I've not checked with Pale Moon, but this setting is
nolonger available in Firefox.

about:config Name: general.useragent.override

Default Value: as per machine's configuration

The ability to change the useragent string via this about:config preferences option - general.useragent.override - to a more common string, may prove to be useful for some users, as the following example may show:

Mozilla/5.0 (Windows; U; MSIE 9.0; Windows NT 9.0; en-US)

(If the required Preference Name is non-existent, creating a new entry requires you to Right Mouse Button click in the about:config page, then by using the RMB menu option ->NEW, a new entry can be created.)

Here is a great useragent string reference page from where you can copy & paste.

Changing this setting can be advantageous in certain circumstances;- like being able to access a site that won't let any other browser than I.E. in. Or fooling sites that your computer is a hand-held so that you get a lighter & faster display, for instance.

As far as using it so as not to stand out in the crowd as a Firefox Linux 64bit user with some other uncommon settings & browser additions is concerned;- if you are taking effective privacy precautions that are mentioned in this thread, it really shouldn't make much difference as the trackers don't know you are there anyway.

On the other hand, if you are doing something on a public wireless network where you would prefer to be untraceable then it would certainly be a good idea to modify your useragent string & then modify it back again when you have finished.

Here is a Firefox add-on called User Agent Switcher that can make this job much easier & quicker for you. You will most likely have to search out additional strings that you can add strings to its menu, which is a nice touch too.

Match Accept Headers to your User Agent String

Works with Pale Moon, though you really do want to
know what you are doing.

about:config Name: network.http.accept.default

Default Value: as per machine's configuration

If you want you can then change the accept headers to match the default for whichever useragent string you went with.

This link is informative.

You can also use the Modify Headers add-on.

OR, if you know what you are doing, you can modify the network.http.accept.default key in about:config.

Enable Spell Checking In All Text Fields

Works with Pale Moon.

about:config Name: layout.spellcheckDefault

Default Value: 1

Possible Values:

   0 - disable spell checker.
   1 - spell check multi-line text boxes only.
   2 - enable spell checker for all text boxes.

The default spell checking function only checks for multi-line text boxes. You can get it to spell-check for single line text box as well.

Which is a great find for me as I'm not a perfect speller.

Open Search Box Results In New Tab

Works in Pale Moon.

about:config Name:

Default Value: false

Modified Value: true

When you search using the search box at the top right hand corner of the browser, it will display the search results in the current tab. If you don’t want the search to interfere with your current tab, you can tweak the to make it open in a new tab.

Speed up Firefox & Pale Moon

This section has grown in the Firefox about:config
I've not researched it, but I am doing some trial
& error.

Two tweaks required for this one;-

Pale Moon has a number of speed tweaks (including this
one) by default.

about:config Name: network.http.pipelining

Default Value: false

Modified Value: true

Works in Pale Moon.

about:config Name: network.http.proxy.pipelining

Default Value: false

Modified Value: true

This combination works for me.

Setting your zoom limit

Works in Pale Moon.

If you find that the max/min zoom level is still not sufficient for your viewing, you can change the zoom limit to suit your viewing habits.

about:config Name: zoom.maxPercent

Default Value: 300 (percent)

Modified value: any value higher than 300

about:config Name: zoom.minPercent Default Value: 300 (percent) Modified Value: any value

Configure Your Backspace Button

Works with Pale Moon.

about:config Name: browser.backspace_action

Default Value: 2 (does nothing)

Modified Value:

Options Are:

   0 - go back to previous page
   1 - page up
   2 - does nothing

In Firefox/Pale Moon, you can set your backspace to better use by getting it to either go back to the previous page or act as page up function.

I set this one to 1 , as my mouse gives me previous page.

Disable Delay Time When Installing Add-on

Works with Pale Moon.

about:config Name: security.dialog_enable_delay

Default: 2000 (in msec)

Modified value:

Options Are:

   0 – start installation immediately
   any other value (in msec)

Everytime you wanted to install a Firefox add-on, you will have to wait for several seconds before the actual installation starts. If you are tired of waiting, you can turn the function security.dialog_enable_delay off so that the installation will start immediately upon clicking.

View Source in Your Favorite Editor

Works with Pale Moon, the 2nd option is not missing
in Pale Moon, which makes it a little quicker to do.

Two modifications required here:

about:config Name: view_source.editor.external

Default Value: false

Modified Value: true (enable view source using external text editor)

about:config Name: view_source.editor.path

Default Value: blank

Modified Value: add the path to your editor here

This is very useful for developers who are always using the ‘view source‘ function. This tweak allows you to view the source code in your favourite external editor.

Middle Mouse Button Paste

Works with Pale Moon.

about:config Name: middlemouse.paste

Default Value: true

Modified Value: false

Turn on/off Middle Mouse Button Paste from Clipboard: "true" or "false" its your choice, so toggle away.

Mouse Scroll Number of lines, plus X & Y control

These work with Pale Moon.

about:config Name: mousewheel.min_line_scroll_amount

about:config Name: mousewheel.default.delta_multiplier_x

about:config Name: mousewheel.default.delta_multiplier_y

The above three about:config lines will allow you to control the amount of x, y & z movement through your mouse wheel.

The only one I changed was the mousewheel.min_line_scroll_amount as I prefer 3 lines to the default of 5 lines.

Browser Tabs Positioning

Only works in Pale Moon - which defaults to false

about:config Name: browser.tabs.onTop

Default Value: true

Modified Value: false

By setting browser.tabs.onTop to false, we are controlling the following:

Not a lot really. Just putting the tab-bar on top of the browser main display field instead of on top of the Navigation bar.

Prevent child windows from spawning

Works with Pale Moon.

about:config Name: dom.disable_window_open_feature.resizable

Default Value: true

Modified Value: false

Turning off the above should prevent most, if not all tabs being spawned in a new Firefox window. Some websites like to do this to us & some of us don't like it!

Disable the least secure encryption protocols

Works with Pale Moon

Setting the above (removed from this page as Firefox has done away with them too) modified values disables RC4 in Firefox. RC4 is the least secure encryption protocol and even Microsoft recommends to disable it.

Just a little more secure are the following encryption protocols. Most encryption experts consider them broken. It is not absolutely necessary to disable them, but it is recommended. If some of the websites you visit via HTTPS/SSL do not work anymore, please enable these protocols again:

about:config Name: security.ssl3.rsa_aes_128_sha

Default Value: true

Modified Value: false

about:config Name: security.ssl3.rsa_aes_256_sha

Default Value: true

Modified Value: false

about:config Name: security.ssl3.rsa_des_ede3_sha

Default Value: true

Modified Value: false

Disable Geo Tracking

Pale Moon defaults to false it uses a more
secure method than the Firefox method of using

about:config Name: geo.enabled

Default Value: true

Modified Value: false

This will disable location sharing.

Highlight everything in the address bar by a single click

Works with Pale Moon.

If you often highlight everything in the address bar to delete it (say, to type in another URL), this setting can save you from having to hit Ctrl+A every time.

about:config Name: browser.urlbar.clickSelectsAll

Modified Value: true


Following is a link to this page's forum counterpart where you can post any related feedback: [6]