1320868 - Moving tabs between Firefox Windows is highly buggy, especially since e10s

Status: UNCONFIRMED

(Firefox :: Tabbed Browser, defect)

Description

[Prasanna]

User Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:50.0) Gecko/20100101 Firefox/50.0
Build ID: 20161104212021

Steps to reproduce:

Drag-move a tab from one Firefox window to another.


Actual results:

Frequently hitting at least one of the following issues:

1. When I try to drag the tab to the Firefox icon on Windows taskbar, I don't see the Firefox windows pop-up sometimes (for me to move it into the window I want)

2. When they do pop up and I mouse over the window I want, the active Firefox window doesn't change to the new guy (screen still keeps displaying the old window)

3. When the screen switch actually happens, and I try to move the tab to the new guy, sadly the tab preview is lost. All I can see I'm dragging is just the cursor (which is even more misleading cause the functionality somehow is not lost yet - the tab move actually happens when I release the cursor)


Expected results:

Should not have seen any of the above glitches while drag-moving the tab.

Comment 1

[Brian Hauer]

I was going to file a separate bug report, but the behavior that I've observed (see below) may be captured by this broader ticket.

When a tab is in a "loading" state, I find it impossible to move the tab between windows. The interactive portion of the drag and drop operation seems to work as expected, but on releasing the mouse button over the destination window's tab bar, the tab in question simply doesn't end up moving.

The tab can be moved once the loading completes and the loading state is cleared.

Comment 2

[Brian Hauer]

Adding to my earlier comment, dragging a tab that is still loading between windows can, in some circumstances, not only fail to drag but also cause the origin window's tab bar to become largely unresponsive. I recently had the following sequence occur:

1. Clicked a URL in Thunderbird, which opened a new tab in an existing Firefox window. But I had two Firefox windows open, and the window automatically selected to receive the new tab was not the window I wanted to use.
2. I started dragging this new tab to the other Firefox window that I wanted it associated with. Despite the conditioning I have developed from experience with tabs failing to move while loading, I nevertheless didn't wait for the tab to complete its load operation.
3. Not only did the tab fail to move (the usual failure mode), but the origin window's tab bar also has decreased functionality. The close buttons on tabs do not work on the window and middle-clicking tabs also does not close them. Only control-W will close existing tabs in this window now.

To recreate this issue, I think it's as simple as this:

1. Find a slow-loading web site.
2. Have Firefox open with two windows.
3. Externally launch a URL to the slow-loading web site you selected.
4. Before the newly opened tab completes loading, attempt to drag the tab from its window to the other Firefox window. Basically you want to attempt this tab drag operation before the tab's hourglass icon goes away.