App Tabs are linked to a window. If you close a window then those tabs get lost if there are other windows still open. If you open a new window then that window doesn't have the App Tabs from other windows.

I'm not on a Mac, but you probably need to exit the Firefox program via "Firefox > Quit Firefox" to make App Tabs stay.

I thought that app tabs would be more persistent, like pinning programs to the taskbar in Windows, but this is not the case.

Instead, once you close a Firefox window, all its tabs and app tabs are lost.

Essentially, this means that the close button in the upper-left corner of a Firefox window is now a "kill all open tabs and loose all App Tabs without warning++ " button. That is not cool.

I realize that "Firefox > Quit Firefox" behaves as intended, but many people use the more obvious red close button instead of the menu to close windows on a Mac. And it is easy to forget that the red button is now also an app-tab-death button. I've lost my app tabs many times to this issue. It is an unforgiving user interface decision which hampers the usability of app tabs. Why should I go through the extra clicks of setting up app tabs if I can loose them so easily?

Ideally, App Tabs could be saved separately from the currently open windows (perhaps create an option to save then to a special Tab Group that opens on startup?). App tabs would be exceedingly useful to me if they weren't so easy to loose.

On that note, saving Tab Groups would also be a useful functionality.

++ You will get a "closing multiple tabs" warning if you have only one window open, and that one window has multiple non-app tabs open, and you have enabled the warning in Preferences. But this too unreliable to help prevent the loss of app tabs.

The pinned apps feature should be fixed so that it works as advertised.

Pinned apps should be retained across sessions (i.e. pinned).

There is a bug where when a second window is opened, it doesn't have pinned apps.

This is a bug not a feature.

And if the first window is closed, and then the second window is closed, when FF restarts there are no pinned apps.

Again, this is a bug not a feature.

It is still happening in FF 4.0.1 for Windows 7. It should be fixed soon, because it affects a lot of people.

I found this answer in another post and it resolves the app tab issue. It's a bit silly though that you can't clear your history but keep your app tabs.

Make sure that you do not use Clear Recent History to clear the "Browsing History" if Firefox is closed because that prevails and prevents Firefox from opening tabs from the previous session.

Solution: (for retaining your Pinned App TABS when using CCleaner) (Note: I’ve only tested this in Windows 7). Firstly, in Firefox, click TOOLS\ADD-ONS, now in the “Search all Add-ons” box (top right of screen) type in “sqlite manager” and press the ENTER key. A list will appear. Select “SQLite Manager 0.7.7” in the list and click INSTALL. No setup is required so close the Add-ons screen now. The following is an essential step if you want your Pinned App Tabs to be retained. In Firefox, click TOOLS\OPTIONS\PRIVACY and select REMEMBER MY BROWSING HISTORY (you can easily set up the CCleaner options to override this setting and clear your history for you, like I have, by simply ticking or unticking the option boxes in CCleaner). After you have finished setting up your basic options in CCleaner (i.e. what to keep and what to clean), while still in CCleaner, select OPTIONS button, select EXCLUDE button, select ADD button, select "Drive or Folder", select BROWSE, now in the box navigate to the following folder. C:\Users\<your username>\ App Data\Roaming\Mozilla\Firefox\Profiles\<filename>.default - Now at the very bottom of the same box select "File Types" and enter sessionstore.js and select the OK button......Your Done.......Enjoy :) PS: You may find that although your Pinned App TABS problem is now solved, after running CCleaner the underlying page of the Pinned App TAB may not display properly in some instances due to the removal (by CCleaner) of cookies necessary for the correct display of that page. If this happens, Open CCleaner, select OPTIONS button, select EXCLUDE button, select ADD button, select "Drive or Folder", select BROWSE, now in the box navigate to the following folder. C:\Users\<your username>\ App Data\Roaming\Mozilla\Firefox\Profiles\<filename>.default - Now at the very bottom of the same box select "File Types" and enter cookies.sqlite - Now select the OK button......and again your Done.......Enjoy :)

OMG fix this bug already! My unborn children can make an array to hold the URLs of the tabs I pin so that they get opened when I restart FF. I'm rapidly losing faith in you guys to develop, while Chrome is looking better and better.