Close Duplicate Tabs on URL Change od Shajirr

When a new tab is opened or current tab URL changes,
this addon will automatically close all the tab duplicates with the same URL.

All the other existing duplicate tabs will not be closed and will be maintained,
until you open an URL that matches them.

Mode selection

The addon has two modes, deciding which tab to keep when closing duplicates:

• Keep the oldest loaded tab (default). Moves the oldest tab to the position of the closed tab. Will still close discarded tabs. The idea is to prevent unnecessary loading of the same page multiple times. Starts closing duplicate tabs right away when new tabs are opened.
• Keep the newest tab. Will wait until no more tabs are being opened, and then will close all duplicates at once. This prevents tab layout thrashing (no tabs are moved), but leads to the content of the same URL being loaded multiple times before the duplicates are closed.

This addon will not close:

• the current active tab
• pinned tabs
• about: pages (various Firefox config/info/utility pages)
• moz-extension: pages (various addon-created pages)
• URLs added to the exclusion list in the addon's Options menu
• specific tabs marked as protected (right click on a page background -> Close duplicate tabs -> keep this tab open)

Other addon functions / settings:

• You can pause/unpause the addon functionality by clicking its button on the toolbar
• URL of the current page can be quickly added to the list of ignored URLs via a page context menu.
• Notifications can be disabled in the Options menu
• You can view up to 20 last closed tab URLs in the History field in Options.

Possible later updates (not yet implemented):

• wildcards for whitelist of URLs that will be excluded from being closed

Permissions

• Access browser tabs - needed to get tab URLs
• Notifications - show notifications