Back IS Close

Back IS Close is a Firefox extension that allows for the convenient closing of tabs or windows.

What it Does | How it Works | Settings | Settings Summary | Comparison to Back To Close | Look and Feel | Privacy Notification | Change Log

Back IS Close has been re-written for Firefox 41, to conform to the Australis UI.

If you have Back IS Close version 1.4 or earlier installed, you MUST manually uninstall it before installing Back IS Close 2.0. If you're using Firefox 2.0, Back IS Close 2.0 won't work for you; keep using Back IS Close 1.4.

To install Back IS Close, first download from the link below, then open the downloaded file in Firefox: Menu | File | Open File...

For Firefox 4.0 - 41.x, download latest version 2.5 (click)

For Pale Moon 25.x, download latest Pale Moon version 2.5 (click)

For Firefox 3.0, download version 2.0 (click)

For Firefox 2.0, download version 1.4 (click)

What it Does

Back IS Close replaces the "Back" button with a "Close" button when the "Back" button is disabled because there is no page to go "back" to. That Close button will close the tab, window, or browser, as appropriate.

Back IS Close is the perfect complement to tabbed browsing: it closes the many tabs tabbed browsing opens.

How it Works

Back IS Close replaces the "Back" button, the Back menu icon on the right-click context menus, and the action of the backspace and Alt-Left Arrow (or Meta-Left Arrow). Replacement is only made when the "Back" button (and other Back GUI elements) are disabled because the current tab or window is on the "back-most" page, and there is no page to go back to.

Using any of these elements will cause the current tab or window to be closed.

In this document, we'll use the "Back" button as shorthand for all these GUI elements, unless otherwise noted.

By default, the replacement is only made on tabs, when a window contains two or more tabs. This is to prevent the accidental closing of a window by using the "Back" button. When the normal Back elements are not replaced, they'll be -- as is normal -- disabled.

Settings Explained

The Back IS Close settings menu can be found in the Add-Ons window, under the list of installed extensions. Just open that window (Main Menu | Tools | Add-ons), select the "Extensions" tab, find Back IS Close in the list of installed extensions, and click the button "Options". This will open the Back IS Close settings window.

You can set Back IS Close to appear on windows as well as tabs. If this is set, windows are only closed after all tabs on that window have been closed. When Back IS Close will close a window, its icon changes to a crossed out window.

You can set Back IS Close to appear on all windows and tabs, on all windows unless that window is the only browser window, or on all windows except the oldest browser window. Limiting the windows the Close button appears on prevents the browser window or Firefox itself from being accidently closed.

Allowing Back IS Close to appear on all windows except the oldest prevents the accidental closing of your "main" browser window. Note that if there is only one window, it must also be the oldest window. This setting prevents you from accidentally exiting Firefox. Non-browser windows (such as the Extensions or Downloads windows) are not counted when determining the number of windows or which is oldest.

Allowing Back IS Close to appear on all windows unless there is only one open window prevents the accidental exiting of Firefox, but doesn't prevent the closing of your main window.

Allowing Back IS Close to appear on all windows means that using the Back IS Close button will exit Firefox if that window is the only open window. If using Back IS Close would close the last window and thus exit Firefox, the Back IS Close icon changes to a doubly-crossed out window.

When any window is closed (by using the Back IS Close button or by any other means), all other windows' Back IS Close buttons are updated. In particular, if closing a window results in only one browser window still being open, the Back IS Close button will either be removed (if your settings don't allow Back IS Close to appear on only the only existing window) or its icon will be change to the doubly crossed-out window icon. Similarly, if your settings don't allow Back IS Close to appear on the oldest window, and you close the oldest window, Back IS Close will be removed from the now-oldest window. And if you change Back IS Close's settings, the buttons will be replaced as needed on all browser windows

Settings Summary

SettingsIf no page to go "back" to, "Back" button is replaced by
TabWindowOldest WindowOnly Window
Tabs OnlyNormal (Disabled) Back Button
Tabs and All Windows except Oldest WindowNormal (Disabled) Back Button
Tabs and All Windows except Only WindowNormal (Disabled) Back Button
Tabs and All Windows
Extension deactivatedNormal (Disabled) Back Button

Compared to Back To Close

Lacking an OS that would run Firefox 3, I didn't update Back IS Close for Firefox 3. Another author created a similar extension, Back To Close. While Back To Close does essentially the same thing that Back IS Close does, there are a few key differences. Back IS Close allows greater selection of what kinds of windows are closed; in particular, it can be set so that the first or only window doesn't close, but other windows do. Back IS Close also changes its Close button, depending on whether a tab, a window, or the whole browser will be closed by clicking it, giving a visual indication of what it will do.

Perhaps most importantly, Back IS Close replaces the Back button when there's no page to go back to. Back To Close shows a Close button in addition to the Back button. I prefer replacement, because adding a button causes the toolbar buttons to the right of the added button to shift to the right. By replacing the button, you don't see any annoying movement, and you can reply on muscle memory to move your mouse to the Back or the Close button in the same way.

Back IS Close goes to a good deal of trouble to try to ensure that the Close button is the same size as the Back button, so that replacement doesn't cause other buttons to shift. But in some cases, that's not possible. See below for why.

Look and Feel

I painstakingly tried to make the Back IS Close button look like the Back button. In particular, Back IS Close mimics the Firefox standard theme's Back button. This is done in large part so that switching tabs doesn't cause the buttons on the toolbar to shift left or right, and some that the toolbar height also remains the same. I find a moving, mutating toolbar to be distracting.

However, in two general cases, this is not possible.

If you set your toolbar to show text labels, since the phrase "Close Tab" is longer than the word "Back", the replacement of the "Back" button with the Back Is Close button will shift the other buttons on the toolbar to the right. If this is distracting, try setting the toolbar to show only icons. In icon only mode, the "Back IS Close" button is exactly the width and height as the "Back" button, so no shifting will be occur.

A work-around for text button sizes is anticipated for the next release of Back IS Close.

If you've installed another Firefox theme, it's not possible for me (for legal and practical reasons) to give you Back IS Close buttons that mimic the theme you've installed. Instead, please contact that theme's author, and ask him or her to add a Back IS Close button to that theme. If the theme authors contact me, I can provide them with some scripts to make creating Back IS Close buttons easy.

With different themes, we have three potential problems. One, the buttons just look different, as they are from different themes. Two, often they are different sizes, so toolbar shifting occurs.

Three, Firefox 3.x introduced the "unified back and forward" button. Back IS Close 2.0 in fact makes itself part of that unified button, so that's not the problem. The problem is that Firefox didn't introduce an explicit setting to turn the unified look on and off.

Instead, the user can select large or small buttons, with text labels, with icons, or with both icons and text. The standard Firefox 3.0 theme decides rather arbitrarily that large icons and small icons-only should use the unified look, and buttons with text (or text and icon) should use the non-unified look. Unfortunately, many theme authors, especially those creating more compact themes, decided not to use the unified look. The practical problem for Back IS Close is that it can tell if the user has selected large or small icons, it can tell if user has selected to have text on the icons, but Back IS Close has no way to determine if the selected icons are an attempt to mimic a unified look.

Partial work-arounds for this issue are anticipated in the 3.0 release of Back IS Close.

The best solution is to ask theme authors to add a Back IS Close button to their themes; a decent solution is for users capable of it to write user.css files that force the particular look they prefer.

Privacy Notification

Back IS Close opens a browser tab to its author's web site when first installed or when a newer version is installed, to provide updated information about Back IS Close to you, and provide debugging information consisting of its current settings to me. No personally identifiable information is transmitted.

Copyright and License

Back IS Close is copyright 2005-2010 TP Diffenbach.

You are granted a limited license to use Back IS Close in conjunction with a Firefox browser. You are granted NO rights to use or reverse-engineer Back IS Close's source code, or to create derivative works.

Change log


Updated for for Australis UI theme. Compatible with Firefox 29.x-41.x.

2.5 (for Pale Moon browser):

Fixed bugs. Compatible with Pale Moon 25.x.


XPICOM component replaced with jsm. XUL, CSS changes. Compatible with Firefox 4.x.


Complete rewrite. Compatible with Firefox 3.x.


Compatible with Firefox 2.0.


Compatible with Firefox


Fixes bug with downloading new version.


Fixes exception message bug on browser start; now interoperable with any extension that calls BrowserBack function.


Compatible with Firefox 1.5.