You can remove the toolbars in all tiled windows using the "Toggle Toolbars" command.

Is this problem still happening?

For multiple pages tiled in a single window try Tile Pages WE.

Yes, but a window manager won't support synchronized scrolling in multiple tabs, or hiding the windows toolbars to increase the viewable page area, or returning the tabs to the original parent window,

Using the new WebExtensions API's, it is not possible to display multiple tabs simultaneously within the same browser window. This is why Tile Tabs WE has to move each tiled tab into a separate window.

Reasons why you might want to use Tile Tabs WE:

• To compare multiple web pages side-by-side.
• To synchronize scroll multiple web pages side-by-side.
• To open links from one tab in adjacent existing tabs.
• To save tiled layouts which can be re-opened for future use.

UPDATE:

Tile Pages WE has just been released and displays multiple web pages in a single browser window!

The reason for tiling inside windows is explained in the 'NOTICES' section at the top of the Tile Tabs WE home page:
https://addons.mozilla.org/en-US/firefox/addon/tile-tabs-we/

Tile Tabs WE does work a little differently to the original Tile Tabs WE, and is not as slick as the original Tile Tabs, but it still meets the same objectives.

- You can still tile as many tabs as you want, either using the pre-defined layouts, or saved custom layouts, or tiling tabs individually (using the Tile Tab or Add Tile menu commands).
- You can simply create a tiled layout by clicking on the toolbar button or by using the Alt+Shift+Up keyboard shortcut.
- You can hide the toolbars in the tiled windows using the Toggle Toolbars menu command or the Alt+Shift+Right keyboard shortcut.

Version 11.1, which has just been released, adds two new features:

- You can select multiple tabs before clicking on the toolbar button to create a layout with just those tiles.
- You can right-click on a tab button and select Tile Tab > Direction to create a layout.

Early versions of Tile Tabs WE retained the original window as the first tile in the the tiled layout, but this design had several problems. For example, if the user used the Toggle Toolbar command, then all of the tabs in the original window (except for the selected tab) would be lost.

Tile Tabs WE is written by the developer of the original Tile Tabs - and can do most of the things that the original Tile Tabs could do.

The main difference is that Tile Tabs tiled tabs in the same window, whereas Tile Tabs WE tiles tabs in separate windows. Features such as opening links in a different tab, synchronized scrolling of tabs, and resizing adjacent tabs are still available in Tile Tabs WE.

The new WebExtensions API's introduced with Firefox 57 must now be used by all add-ons and do not support displaying multiple tabs in the same browser window.

There is very little that the old Tile Tabs could do, that Tile Tabs WE cannot do. The main difference is that the old Tile Tabs tiled tabs in the same window, whereas Tile Tabs WE tiles tabs in separate windows. Features such as opening links in a different tab, synchronized scrolling of tabs, and resizing adjacent tabs are still available in Tile Tabs WE.

The new WebExtensions API's introduced with Firefox 57 must now be used by all add-ons and do not support displaying multiple tabs in the same browser window.