

You can use the Nightly pre-release channel to start testing how your themes will look with Firefox 89. (Note: users will need to enable the separator by right clicking on the bookmarks toolbar and selecting “Add Separator.”) You can still use this property to control the separators in the bookmarks toolbar.

The property toolbar_vertical_separator, which controls the vertical lines near the three-line “hamburger menu” and the line separating items in the bookmarks toolbar, will no longer appear next to the hamburger menu.The property toolbar_field_separator, which controls the color of the vertical line that separates the URL bar from the three-dot “meatball menu,” will no longer be supported.In Firefox 89, this property will set a color for all borders of an active tab, and the borders will be thinner. Currently, the tab_line property can set the color of an active tab’s thick top border.The property tab_background_separator, which controls the appearance of the vertical lines that separate tabs, will no longer be supported.Since some of the changes will affect themeable areas of the browser, we wanted to give theme artists a preview of what to expect as the appearance of their themes may change when applied to version 89. Firefox’s visual appearance will be updated in version 89 to provide a cleaner, modernized interface.
