Firefox Tips & Tricks

Enable closing of last open tab (enable close icon in last tab)
1. Open about:config
2. Set browser.tabs.closeWindowWithLastTab pref to false

Color active tab
1. Create a folder named chrome (if not present) in %APPDATA%\Mozilla\Firefox\Profiles\{profile_name}
2. Type "resource:///chrome/browser/skin/classic/browser/browser.css" in addressbar and hit Enter
3. Search for the text (CTRL+F) ".tabbrowser-tab[selected="true"] {"
4. Open notepad and add the above block and add !important to override the defaults.

.tabbrowser-tab[selected="true"] {
background-image: linear-gradient(rgba(255,0,0,.7), rgba(255,0,0,.5) 50%),
linear-gradient(-moz-dialog, -moz-dialog) !important;
}

5. Save it as userChrome.css in the chrome folder.

Force open pop-ups in new tab
1. Open about:config
2. Set browser.link.open_newwindow.restriction pref to 0

Reference - http://kb.mozillazine.org/Browser.link.open_newwindow.restriction

Open in background tab in Right click --> "Search Google for"
1. Open about:config
2. Set browser.search.context.loadInBackground pref to true

Increase number of Previously Closed Tabs
1. Open about:config
2. Set the value of browser.sessionstore.max_tabs_undo pref to your desired value

Increase number of Previously Closed Windows
1. Open about:config
2. Set the value of browser.sessionstore.max_windows_undo pref to your desired value