Context
People doing real work in a browser — research, multi-project tracking, anything spanning more than a handful of tabs — were fighting a flat, linear tab bar that hadn't fundamentally changed in over a decade, while the amount of parallel context people asked a browser to hold had grown enormously.
My role
I set the UX strategy and led the design team responsible for Firefox's core navigation and multitasking surfaces — Sidebar, Vertical Tabs, Tab Groups, and Split View — and mentored the surface's long-term owner into becoming the domain expert other teams (including Smart Window and Nova) still turn to years later when their work touches core browser architecture.
The hard call
Vertical Tabs meant asking people to relearn a decade of muscle memory, for users who hadn't asked for the change. We treated it as an opt-in, quality-first bet rather than a forced migration — investing in getting the interaction model right (grouping, pinning, hover previews) before pushing for broader adoption, rather than shipping fast and asking people to adapt.
Outcome
Draft note: the numbers below are sourced from internal 2025 H2 performance documentation, not previously made public. Confirm you're comfortable publishing them before this goes live.
The surfaces have stayed durable well past initial launch — actively maintained, still the reference point other teams building new Firefox surfaces go to for how core navigation should behave, with Tab Groups shipping as a natural extension of the same model.