Firefox night assemblies laid the foundation for the release of Firefox 129 on August 6. The new version introduced a side panel implementation and the option for vertical placement of tabs. This feature is particularly beneficial for users with large-format screens, as it allows them to utilize additional screen space to view website content. Vertical tabs had been under testing in separate LARCH assemblies since April and are now available in regular night assemblies. To activate vertical tabs, users need to enable the parameters of Sidebar.revamp and Sidebar.verticaltabs on the ABOUT:Config page.
The side panel can be displayed in both detailed and condensed forms. In the detailed view, page headings in the tabs and operation names are visible, while only icons and operations are shown in the condensed mode.