My Favorite Firefox About:config Tweaks

Type About:config in URL bar to get there then it says something about Firefox having a warranty click the "I'll be careful,I promise" to continue.

To change a value just double click it or right click then modify. Once done just restart the browser as some changes do need one to take effect.

1) Spell checker more checky
layout.spellcheckDefault
0 disable
1 default
2 for all text typed to be spell checked

2) Open search results in a new tab
browser.search.openintab
set to true
default false

3) Disable Add-on install delay
security.dialog_enable_delay
set to 0 or if you wish to increase set to any amount of milliseconds
default 2000

4) Preview Tabs With the CTRL+TAB switcher(similar to windows ALT+TAB)
browser.ctrlTab.previews
set to true
default false

5) Add More Rows and Columns to Firefox's New Tab Page
browser.newtabpage.rows
browser.newtabpage.columns
and set how many to each
default 3 for both

6) Get the old download window for Fierfox17+ Removed fully in 26
browser.download.useToolkitUI
set to true
default false

7) Show or hide the close buttons on a tab
browser.tabs.closeButtons
0 – display a close button on the active tab only
1- display close buttons on all tabs
2- don’t display any close buttons
3- display a single close button at the end of the tab strip

8) Auto export bookmarks
browser.bookmarks.autoExportHTML
set to true to auto export bookmarks

9) Get more Add-on search results
extensions.getAddons.maxResults
default 15 set to what you want

10)Bring back the Save tabs and quit button
browser.showQuitWarning
set to true
default false

11) Options menu not flashy enough
browser.preferences.animateFadeIn
set to true and watch
default false

12) Tabs below URL bar Firefox 15+ removed easy access to this
browser.tabs.onTop
set to false
default true

13) IE like Quick Tabs aka all tabs previews
browser.allTabs.previews
set to true
default false

And all of this can be undone just as easily should you want to revert the changes.