User Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:52.0) Gecko/20100101 Firefox/52.0 Build ID: 20161107030203 Steps to reproduce: TEST SCENARIO A 1. Install Tile Tabs WE 5.1 - https://addons.mozilla.org/en-US/firefox/addon/tile-tabs-we/ 2. Open a browser window 3. Create three tabs (all Wikipedia home page) 4. Click the Tile Tabs WE button to create a layout with two tiled browser windows, each containing one tab from the original browser window. 5. Click the Tile Tabs WE button in one of the two tiled browser windows, which closes both of the tiled browser windows by moving the last tab in each tiled browser window back into the original browser window. TEST SCENARIO B 1. Install Tile Tabs WE 5.1 and Zoom Page WE 3.2 - https://addons.mozilla.org/en-US/firefox/addon/zoom-page-we/ 2. Repeat steps A2 to A5. Actual results: TEST SCENARIO A Tile Tabs WE uses chrome.tabs.move() to move the last tab out of each tiled browser window, which results in the following error message: TypeError: win is null[Learn More] URLBarZoom.jsm:24:7 I suspect this error is due to the zoom change observer calling updateZoomButton() after the tiled browser window has closed. TEST SCENARIO B Zoom Page WE has a chrome.tabs.onZoomChange.addListener() listener, which results in the following additional error messages: Unchecked lastError value: Error: Invalid tab ID: 6 ExtensionUtils.jsm:399 withLastError resource://gre/modules/ExtensionUtils.jsm:399:9 wrapPromise/< resource://gre/modules/ExtensionUtils.jsm:450:11 I suspect these errors are due to the zoom change listener being called after the browser window has closed. I have no idea where the invalid tab ID (6) comes from, since there are only three tabs in the original browser window. Expected results: TEST SCENARIO A There should be no error messages. TEST SCENARIO B There should be no error messages.

It is a dupe of bug 1297970 which should be fixed by bug 1300376.

The bug I reported has a wider scope than bug 1297970 or bug 130076, both of which are focused on calls to updateZoomButton() - my 'Test Scenario A'. As far as I can see, the fix for bug 1300376 does not address calls to chrome.tabs.onZoomChange listeners - my 'Test Scenario B'. Please can you confirm whether 'Test Scenario B' is addressed by the fix for bug 1300376.

Let's reopen it and check when bug 1300376 will be fixed.

I will re-test when bug 1300376 is fixed. I am pretty sure the changes for bug 1300376 will not fix my Test Scenario B.

de-dev: can you verify?

I have repeated the Test Scenarios A & B, using Tile Tabs WE 5.1 and Zoom Page WE 3.2, and the error messages do not appear. I have also repeated the Test Scenarios A & B, using the latest versions of my add-ons (Tile Tabs WE 9.2 and Zoom Page WE 10.4), and the error messages do not appear. As far as I am concerned, this bug is fixed.

Bulk move of bugs per https://bugzilla.mozilla.org/show_bug.cgi?id=1483958