Firefox 156 starts its built-in PDF viewer up to 45% faster
Serguey Asael Shinder2 min readFirefox 156.0 reached the release channel on 15 September. The notes are at https://www.mozilla.org/en-US/firefox/156.0/releasenotes/ and the performance entries are the ones worth reading.
The built-in PDF viewer now starts up to 45% faster. Memory and CPU use improved when the browser displays large JPEGs scaled down to fit a page — the common case for any site that serves a full-resolution photo into a thumbnail slot. And on Windows machines with ARM64 processors, WebRTC video calls can now use hardware H264 decoding instead of falling back to software, which on those machines is the difference between a call that costs battery and one that costs the whole battery.
Two of the fixes describe outages rather than annoyances. Some sites failed to load entirely when DNS over HTTPS was enabled and the site did not support HTTPS; and some users with the built-in VPN enabled lost all network connectivity. Both are the kind of defect that gets reported as "the internet is broken" rather than as a browser bug.
The rest is housekeeping: macOS can start Firefox at login from the Startup section of Settings; localized Wikipedia and occasional sponsored suggestions arrive in the address bar in France, Germany and Italy, switchable off in Firefox Suggest settings; and there are fixes for dragging images in rich-text editors, high-sample-rate FLAC in MP4, subtitles in Picture-in-Picture, bookmark folders, and a find bar that became permanently unavailable after reversing the panes in Split View. Plus the usual security fixes.
What it means
A 45% faster PDF start is a bigger user-visible win than most feature releases. Browsers open PDFs constantly — invoices, tickets, statutes, forms — and the startup path is the part a person actually waits on. It is also the kind of improvement that never makes a headline, because it is not a feature and cannot be demonstrated in a screenshot.
The DNS-over-HTTPS fix is a reminder about layered defaults. DoH is on by default in many configurations, and a site that does not support HTTPS is not an exotic case — it is a router admin page, a printer, an old intranet host. When a privacy default and a legacy endpoint meet, the failure lands on the user as "this site is down", with no signal that a browser setting caused it.
And hardware decode on ARM64 Windows is the quiet story of the year. Windows on ARM is no longer a curiosity, and every codepath that still falls back to software on those machines is a battery-life bug waiting to be filed. Expect more of these entries, in more applications, for the next several releases.