How to Un-Hide Firefox’s Vertical Tabs/Sidebar

The square button with the one side heavier than the other is the Sidebar button. By default, it is placed to the left of the Back/Forward buttons. It always opens the Sidebar, even if it is hidden. The blue-on-hover cue does… nothing, actually.

This comes about because I clicked “Hide sidebar and tabs,” closed the configuration, and then realized I had no idea how to open the sidebar. There was a hover cue, but I couldn’t figure out how to interact with it! KDE just wanted to resize the window.

After experimentation with the Sidebar options—the options reachable through the gear icon on the Sidebar itself—I think I understand the logic behind it.

There are three visibilities of the Sidebar:

• Hidden: it is not displayed at all.
• Closed: it is a narrow, icon-wide column.  If Vertical Tabs are on, the tabs are icon-only, with no text.
• Open: it is a tab-width column; the tabs have the page’s title text, just like horizontal tabs do. This visibility is only accessible when Vertical Tabs are on.

Then, in all cases, clicking the Sidebar button expands or shrinks it, relative to the current configuration.  That means:

1. Horizontal Tabs: It switches between Hidden and Closed.  There are no tabs in it.  Open is not possible, and the options are not selectable.
2. Vertical Tabs with no other options: It switches between Closed and Open.  Hidden is not possible.
3. Vertical Tabs with “Expand sidebar on hover” option: nearly identical to the previous, except that hovering the Closed sidebar with the pointer will Open it for the duration. The Sidebar button can be interpreted as “Keep Open” vs. “Open on Hover” in this case.
4. Vertical Tabs with “Hide sidebar and tabs” option: It switches between Hidden and Open. Closed is not possible.

Although the interface presents check boxes for both of the options, it is actually the case that “Expand sidebar on hover” and “Hide sidebar and tabs” are mutually exclusive. Choosing either of them deactivates the other. We used to have a standard interface for this sort of thing.

Just sayin’.