You have to know that “About:config” page lets you change almost every aspect of how Firefox functions. Going through and explaining what every preference does would not only be an impossible task, but also unnecessary since most people are happy with the default settings. There are, however, a few settings that we think are essential to change. Make these tweaks first when you encounter a fresh install of Firefox.

Here the list:

browser.urlbar.autoFill = True
Enable auto-complete for URLs when typing into the location bar.

browser.sessionstore.max_tabs_undo = 15
Increase the number of closed tabs that firefox has stored in its cache to 15.

browser.tabs.tabMinWidth = 75
Show more tabs in a single window by narrowing the minimum width of a tab.

browser.search.openintab = True
Automatically open new search results in a new tab

middlemouse.paste = True
Use the middle mouse button to paste text from your clipboard.

browser.blink_allowed = False
Disables annoying text with the Blink tag.