[tylertylerday]

Discussion: #10336

Ctrl+Tab, Ctrl+Page Down and Ctrl+Page Up are handled by Firefox in ShortcutUtils.getSystemActionForEvent rather than through <key> elements, so they can't be changed in about:keyboard. This adds disabled <key> elements that only hold their bindings (zen-tab-switcher-cycle, -next and -previous), so they show up in about:keyboard like any other shortcut. Until one is customized, Firefox's built-in shortcuts apply unchanged, including the macOS variants. Once it is, ZenKeyboardShortcuts.getSystemActionForEvent matches the new binding in tabbox.js and browser-ctrlTab.js, and the built-in one stops working. When cycling in recently used order, the panel picks a tab when the custom shortcut's modifier is released, and Shift still goes backwards unless the shortcut uses Shift itself.

In about:keyboard, these three are in a new Tabs category right after Navigation, together with Firefox's Select Tab 1–8 and Select Last Tab, which move there from Navigation.

Settings → Tab Management gets a Tab Switcher section with the Ctrl+Tab options: Firefox's "recently used order" checkbox (moved from General), the existing pending and essential tab options, and a new option to cycle through the tabs of every space instead of only the current one (zen.tabs.ctrl-tab.cross-space, off by default). Picking a tab from another space switches to that space. The labels show the current shortcut, and the description links to Keyboard Shortcuts. Because those strings now take the shortcut as a variable, they have new Fluent IDs.

Tested on a local Linux build. I added browser tests for remapping, clearing and resetting the shortcuts, the about:keyboard category, and cross-space cycling. The kbs, browser_ctrl_tab_cross_space.js and browser_tabs_cycle_by_attribute.js tests pass, and npm run lint is clean.

[tylertylerday]

Changed the shortcut between screenshots, so ignore the discrepancy.