Firefox Desktop OSs about:config Modifications

In the following examples you will need to access Firefox's hidden configuration page by setting in the address bar type 'about:config' (without the '') and press 'Enter', then click the 'I'll be careful, I promise' button.

To the right of 'Config name:' is the value to copy and paste in the 'about:config' 'Filter' bar.

To the right of 'Default:' is the original value.

To the right of 'Modified:' is the new value.

HOWTO: Remove New Tab Thumbnails
You can create these Boolean preferences on the about:config page if you want to prevent Firefox from generating thumbnails for the about:newtab page.

name: browser.pagethumbnails.capturing_disabled with value: true name: pageThumbs.enabled with value: false

You need to delete the thumbnails folder in the Firefox profile folder to remove already stored web page thumbnails.

HOWTO: Remove The New Tab Page
about:config > browser.newtab.url > about:newtab > about:blank

Default Value = about:newtab

HOWTO: Change The Colour Colour Of The Pin Tab Highlighting
~/.mozilla/firefox/5rdkbk74.NEW/userChrome.css

.tabbrowser-tab[pinned][titlechanged]:not([selected="true"]) { background: -moz-linear-gradient(hsla(0,0%,100%,.2), hsla(0,0%,45%,.2) 2px, hsla(0,0%,32%,.2) 80%) !important; } .tabbrowser-tab[pinned][titlechanged]:not([selected="true"]):hover { background-image: -moz-linear-gradient(hsla(0,0%,100%,.6), hsla(0,0%,100%,.2) 4px, hsla(0,0%,75%,.2) 80%) !important; }

http://forums.mozillazine.org/viewtopic.php?f=38&t=2486171

Address (URL) Bar Search Provider - Change: How To
NOTE: If you have installed the correct version of Firefox for your locale you should not need this tweak, and the key will not be present. To check in about:config search on 'useragent.locale' to confirm, for the UK you should have 'en-GB'.

The above example is for Google UK but of course there are other search engines, however they do not all use the same format. Here are a couple more:

http://www.bing.com/search?q= http://search.yahoo.com/search?p=

Address (URL) Bar - Select All Text With One Click: How To
 Windows 

 Linux 

 Apple 

Double click to toggle the value.

AV Format Support - Disable (v.29>)
Linux users may play Mp3, AAC and H.264 contents in the web browser without plugins:

Double click to toggle the value.

AwesomeBar: Change The Amount Of Results Returned (v3 >)
The "AwesomeBar" allows you to do a keyword search of your bookmarks, tags and browsing history by typing in the address window. As you start typing in the address bar the AwesomeBar shows you a list of a dozen suggestion, this tweak allows you to set a higher or lower number of returns.

Double click and alter to your choice.

Backspace Button - Change Behaviour: How To
Double click and alter to your choice.

Click-To-Play - How To Enable (Firefox 15 -->)
Prevents some plugins from automatically playing content.

Context Search - Change Search Provider: How To
This is when you highlight a piece of text and right click (context menu) then search. By default Firefox uses Google.com if you want to change it to another make sure you have that search engine provider installed.

Extension Install Delay - Alter Or Disable: How To
Double click and alter to your choice. A value of '0' disables any delay.

Image Resizing - Disable: How To
If on opening a link to an image file it is too large to fit on screen by default Firefox reduces it to fit it all on screen. The following tweak disables this behaviour.

Double click to toggle the value.

Location Aware Browsing (a.k.a. Geolocation) - Disable: How To (v3.5 >)
Firefox uses its default geolocation service provider (Google) to determine the location of your computer using the following:


 * the computer’s internet IP address
 * information from nearby wireless access points
 * a random client identifier (this is assigned by Google and expires every 2 weeks).

If you are concerned about your privacy this feature can be turned off in the following manner:

Double click to toggle the value.

Menus Slow To Open - Speed Them Up: How To
In a blank area of the configuration window, right click:

Middle Button (Scroll Wheel) Paste
Linux

Windows

Apple

Double click to toggle the value.

Plugins - Controlling (version 22 -->)
Plugins for programme extensions such as Adobe Flash would have their status changed from disabled to enabled after installation of a new version of Firefox. From version 22 of Firefox this will no longer happen, control of plugins has been moved from pluginreg.dat file to about:config.

Prevent Firefox From Closing When Shutting The Last Tab: Enable (v3.5 >)
Double click to toggle the value.

Prevent Firefox Stealing Focus When Opening Browser Links In An Email Client
NOTE: This fix requires alteration of Firefox's about:config settings not Thunderbirds

If Firefox is your default browser then when you click on an URL in Thunderbird it is opened and Firefox springs to the forground.

To prevent this open Firefox's about:config and alter the following.

Double click to toggle the value.

Session Restore Function - Alter Saving Frequency: How To
Double click and alter to your choice, 1000 equals 1 second so 60000 equals 1 minute.

Tabs - Save On Exit: How To (v.4 >)
By default FF4 does not offer to save open tabs when closing, this is a regression back to FF2 days. To turn on this option look under:


 * Windows - Tools --> Options --> Tabs: Warn me when closing multiple tabs
 * Linux - Edit --> Preferences --> Tabs: Warn me when closing multiple tabs
 * Apple - Edit --> Preferences --> Tabs: Warn me when closing multiple tabs

If for any reason you find the corresponding box ticked but Firefox is still closing without the requisite warning try the following:

If the above does not work check that the following all have their values set to false:

Zoom Limits - Setting: How To
The maximum increase in size can be altered:

Likewise the decrease in size can be altered:

HOWTO: Prevent Websites From Reading or Modifying Clipboard Contents
For why you would want to see the following article at ghacks.net