Most useful Mozilla Firefox about:config tweaks

Since its inception Mozilla and has remained highly customizable. In addition, applications run by it can also be configured as per users’ preferences. about:config is a feature of Mozilla that gives access to advanced settings, hidden under the browser. These settings aren’t available in the browser’s standard options window.
To access Firefox’s advanced settings, simply type about:config into the browser’s address bar and press Enter. Thereafter, you should see a warning page. Hit the ‘I’ll be careful, I Promise’ button and proceed towards tweaking Firefox about:config settings.

Firefox about:config tweaks

Let us have a look at some of the most useful Firefox about:config tweaks.
1] Open New Tabs at End
Normally, every new tab appears adjacent to the current tab, however, if you would like the tab to open at the end of all the tabs, do the following.
Look for browser.tabs.insertRelatedAfterCurrent and change the value to False. Default value is set as True.
2] Preview Tabs When Switching
To enable previews feature in Firefox, go to browser.ctrlTab.previews and change the default False value to True to view previews.
3] Disable Prefetch of Webpages
An ingenious feature to help pages load faster but problem encountered, consumes large part of bandwidth. As such it is best to keep it off when you have slow Internet connection. How you do it? Look for network.prefetch-next and switch to FALSE value.
4] Increase Network Performance
For enhancing the network performance, search for network.http.max-connections. It manages maximum network connections the browser can make at one time to any number of Web servers. The latest version of Firefox supports 256. If you find the same value, do not change. If not, change it to the defined value.
Find network.http.max-persistent-connections-per-server and change it from 6 (default) to 7 or maximum, 8.
5] Turn off the URL greying
Assuming you have about:config Page opened, search for: browser.urlbar.formatting.enabled

Double-click it to change it to False. Now, you should find the URLs displaying address in black text. Also, Firefox hides ‘HTTP’ in URLs so that they are easier to read. If you do not like it and would like to unhide the “http” portion of a URL, search for browser.urlbar.trimURLs and Double-click the setting to change it to False. That’s it!
6] Make Firefox’s Spell Checker More Useful
To enable Firefox Spell Checker in all text boxes, search for: layout.spellcheckDefault and set its value to 2. Now, to make those line more noticeable, right-click in empty space of about:config page, Select New > Integer, and name it: ui.SpellCheckerUnderlineStyle.
Thereafter, configure its value to

1. 0 for no highlighting
2. 1 for a dotted line
3. 2 for long dots
4. 3 for a single straight line
5. 4 for a double underline
6. 5 for the default squiggly line

7] Add More Rows and Columns to Firefox’s New Tab Page
Simply move to about:config and search for: browser.newtabpage.rows. Then, browser.newtabpage.columns and set each to the value you want. You will now be given the choice to accommodate more sites on that new tab page.

 

Select all text when click on the URL bar
Head to browser.urlbar.clickSelectsAll and Modify value.
False – place cursor at insertion point
True – select all text on click
Same Zoom Level For Every Site
If you want the zoom level to remain same for every website you visit via Firefox browser, simply toggle the value of browser.zoom.siteSpecific from True to False. Default value is set to True.
8] Disable Compatibility Checking for Extensions
Open about:config and right-click on an empty space. Choose New > Boolean and create a new setting called: extensions.checkCompatibility.
Set its value False.
9] Disable Animations for New Tabs
To disable animations for new tabs, Firefox’s “Tab Groups” feature, find  and set the first two of these to False
browser.tabs.animate
browser.panorama.animate_zoom
browser.fullscreen.animateUp
10] Bookmark About:Config
Bookmark About:Config with Ctrl+D. Open Bookmarks with Ctrl+B and find the new bookmark.
Right-click its properties. Give it a short keyword. For instance, I use “AC”. Now there ir no need to type about:config again

Source: http://www.thewindowsclub.com/mozilla-firefox-about-config-tweaks