Mozilla has shipped Firefox 155, and it's a milestone release: this is the first version under Firefox's new two-week release cadence, arriving two weeks ahead of the originally planned September 15 date. If you've got automatic updates on, you're probably already running it.
What's New
Smart Window expands and gets faster. Firefox's AI-assisted browsing feature, Smart Window, is now available to all users in the US, Canada, and France. The Assistant responds noticeably faster and now cites its sources when it pulls in web search results via Exa. Organize Tabs, the auto-grouping feature, also got smarter — it suggests better tab groupings and gives each group a clearer, more descriptive name.
Web standards support grows. Firefox 155 adds support for QUIC version 2 (RFC 9369) for HTTP/3 connections, along with two new WebAssembly proposals: Compact Import Section (which shrinks module size for sites with many imports) and Wide Arithmetic (128-bit math instructions that speed up cryptography and precision math workloads).
Everyday usability improvements. Tab groups can now be sorted, containers can be reordered right from Settings, and the address bar can show how many trackers it has blocked on the current page. Firefox also gained support for Nintendo Switch Pro controllers and for Happy Eyeballs v3, which should make page loads feel snappier on dual-stack networks.
Developer tools. The Rules View in DevTools now has toggles to emulate prefers-reduced-motion, the Debugger got a shortcut to enable/disable all breakpoints at once, and the JSON Viewer can now display JSON Lines (JSONL/NDJSON) documents.
Security and stability. This release patches more than 30 security vulnerabilities, and fixes a longstanding bug that prevented some Linux systems from going to sleep after an extended browsing session.
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