Some serve same basic purpose, but only use one at a time. Uncertain which I prefer or haven't found better ones. Divided into Currently Installed, Uninstalled or Disabled, & Interesting Add-ons.
A simple extension that counts the number of open tabs per window and displays the count in the toolbar...
Simply adds "Duplicate Tab" to tab context menu.
This extension will automatically close old windows and tabs so you don't wind up with zillions of old windows open at the same time. NEW FEATURES IN 3.0. Password protection....and 3 modes of operation.
Double-click action for Firefox -
double-click Link, Bookmark/History to open in new tab (emulate ctrl+click).
Quickly and easily increment and decrement numbers and strings in URLs for navigating through URL sequences.
Keep your menus in check by filtering out items you never use.
Take control of your tabs! Purposely lightweight extension with the following features...
Replaces the "Undo Close Tab" menu item with the "Recently Closed Tabs" submenu.
Adds "Open Link" menu to force links to open in current tab.
Add "Undo" and "Redo" menu in context menu of bookmarks.
Automatically shows trimmed content in Google Mail™.