Firefox Desktop OSs about:config Modifications

In the following examples you will need to access Firefox's configuration page by setting in the address bar type 'about:config' (without the '') and then press enter, followed by clicking 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.

To modify a true/false config state double click on the Config name.

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

Firefox Stealing Focus When Opening Browser Links From An Email Client
If Firefox is your default browser then when you click on an URL in Thunderbird it is opened and Firefox springs to the foreground.

Image Resizing
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.

Location Aware Browsing (a.k.a. Geolocation) (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:

REFERRER CONTROL
Alternative:

If you have trouble accessing say a banks website try the following configuration instead:

SSL3
Below are the settings to manually disable SSL3 protocols that are now considered insecure. While this can be done manually the latest versions of Firefox should disable them automatically and you can check this by looking at the following:

You can test the SSL safety of your browser at Poodle Test.

If you are completely paranoid and do not trust the above setting the following can be changed manually:

The following are considered to be slightly more secure but if erring on the side of caution modify them as well:

Websites From Reading or Modifying Clipboard Contents
NOTE: This is a biggy, if you regularly copy text from inside a form field then this tweak is not for you.

For why you would want to see the following article at ghacks.net

Autoscrolling (or Middle Button Scrolling)
Linux

Windows

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

HTML 5 PLAYER SUPPORT
Lastly check the following (mine was false by default):

Note: See also WEBM Support

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

Prevent Firefox From Replacing Tabs When Using "Open All in Tabs"
When opening a folder of bookmarks using "Open All in Tabs", the currently displayed tabs are replaced. Creating this preference and setting it to 'True' will cause the new tabs to opened along side the current tabs.

PRIVACY TRACKING PROTECTION
Thanks to Ghacks

TABS >> SAVE ON EXIT SHOW/QUIT WARNING ON EXIT
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:

New Tab Thumbnails
Create the following two Boolean preferences if you want to prevent Firefox from generating thumbnails for the about:newtab page.

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

Address (URL) Bar Search Provider
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
 Windows 

 Linux 

 Apple 

Amount Of AwesomeBar Results (v.3 >)
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.

Awesomebar Suggestions
When you type something into the Awesomebar, Firefox ranks its suggestions by something it calls "Frecency," a combination of how frequently and recently you visited a given URL. However, you can adjust the "weight" it gives to certain types of URLs—like bookmarks—with a few about:config tweaks.

For example that you wanted to give bookmarks a higher weight (so Firefox is more likely to suggest them near the top of the list) or no weight (so you don't see bookmarks at all in the Awesomebar suggestions).

The default value is 140, so if you want bookmarks to rank higher. increase this number. If you want them to rank lower, decrease this number, or set it to 0 to eliminate bookmark suggestions entirely. For more information, check out Mozilla's developer page and Knowledge Base article on frecency settings.

Mercilessly filched from here.

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; }

The above was pulled from here.

Context Menu Search Provider
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
Double click and alter to your choice. A value of '0' disables any delay.

Middle Button (Scroll Wheel) Paste
Linux

Windows

Apple

Double click to toggle the value.

Plugins Control (v. 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.

Session Restore Frequency
NOTE: 1000 equals 1 second so 60000 equals 1 minute.

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

Likewise the decrease in size can be altered: