Firefox 153 Merges PDFs for Free, Undercutting a Billion-Dollar Market

Firefox 153 shipped July 21, 2026, carrying a feature that quietly threatens a slice of the software industry: drag-and-drop PDF merging, done entirely on your own machine. No uploading a document to a stranger’s server. No account. No fee. Mozilla built the feature straight into the browser.

The company has done something like this before, in reverse. A year earlier, Mozilla shut down Pocket and Fakespot, two products it once championed, citing limited resources. Firefox 153 shows where those resources went instead: into features that live entirely in the browser’s own code, at the expense of anything that needed a server to survive.

How Firefox’s PDF Sidebar Merges Files Now

The mechanics are simple. Open a PDF in Firefox, expand the built-in sidebar, then drag another PDF onto it. Firefox appends the new pages to the open document instead of launching a separate app or sending the file to a third party’s servers. Individual images can be dropped in too, turning a scanned signature page or a cover sheet into a new page inside the same file.

1. Open the PDF you want to build on in Firefox’s viewer.
2. Expand the sidebar showing page thumbnails.
3. Drag another PDF, or a single image, onto the sidebar to append it as new pages.

Selected text now renders with higher contrast and follows the operating system’s own color settings, a readability fix rather than an editing one.

The drag-and-drop motion is what’s actually new in version 153. Firefox gained PDF merging two releases earlier, in May, but that version required clicking through a file picker to choose the second document, according to OMG Ubuntu’s coverage of the update. Mozilla has been building this tool in stages rather than launching it all at once, which is easy to miss if the changelog is all you read.

The Multibillion-Dollar Market Firefox Just Undercut

The category Firefox stepped into is not small. GlobalGrowthInsights, a market research firm, sizes the global PDF editor software market at $5.55 billion in 2026, projected to reach $24.96 billion by 2035. A large share of that runs through free-to-use, ad-supported websites, the kind that ask a user to upload a document, wait while it processes on a remote server, then download the result, often behind a signup wall past a few files a day.

That upload step is exactly what worries a meaningful slice of the audience. A separate GlobalGrowthInsights study found that 28% of users worry about data breaches and unauthorized access when using online PDF tools. Firefox’s version skips the upload step entirely. The file never leaves the device, so there is nothing sitting on someone else’s server to leak.

Firefox does not touch OCR (optical character recognition) or e-signatures. It touches the single most common reason people visit those sites in the first place: sticking a couple of files together.

Containers Leave the Add-On Store for Good

PDF tools are not the only outside category Firefox absorbed this release. Multi-Account Containers, an official Mozilla extension that let users log into the same site under separate identities in color-coded tabs, is now a native part of the browser. OMG Ubuntu called containers the single biggest user-facing feature in the update.

The idea is to keep work, banking, and shopping logins apart inside the same window. Each container isolates its own cookies and ad tracking, so activity in one stays invisible to trackers running in another, according to Mozilla’s own release notes.

An extension that power users installed by hand for years is now something everyone gets by default, no add-on store required. It is the same shape as the PDF move: take a job a separate piece of software used to do, and fold it into the browser for free.

Why Mozilla Killed Pocket to Fund Features Like This

Mozilla’s own history explains the pattern better than any changelog. In May 2025, the company announced it was shutting down Pocket, its read-it-later app, and Fakespot, its fake-review detector, effective that summer.

But the way people save and consume content on the web has evolved, so we’re channeling our resources into projects that better match browsing habits today.

Mozilla wrote in the blog post announcing both product closures. Pocket, which Mozilla had acquired in 2017, stopped working on July 8, 2025. User data was deleted that October.

Both products needed servers, subscriptions, and ongoing maintenance to keep running. PDF merging and tab containers need none of that. They run on code already sitting on a user’s machine. Mozilla is not just adding features. It is trading products that cost money to operate for ones that do not.

The instinct to keep files off someone else’s server is not paranoia. Only months earlier, the hacking group ShinyHunters had been holding 275 million student records hostage after pulling them from Instructure’s Canvas platform, a reminder that anything uploaded somewhere else can end up somewhere it should not.

Can Firefox Replace Adobe Acrobat for PDFs?

Only partly. Firefox 153 covers one task well: combining files without a subscription. It still has no OCR to make scanned pages searchable, no e-signature workflow, no compression tool, and no way to split one PDF into several, the features that keep paid suites and premium tiers in business.

• OCR – no built-in way to turn a scanned page into searchable, selectable text.
• E-signatures – no legally binding signing workflow; users still need a dedicated service.
• Compression – no option to shrink an oversized PDF before emailing it.
• Splitting – no way to pull one page out of a larger file inside the browser yet.

Those four gaps are exactly what keeps Adobe Acrobat, Nitro, and their subscription peers in business, even as the free, everyday task of sticking two files together quietly moves into the browser at no cost.

Mozilla Packs In HDR Video and a Faster Update Clock

Firefox 153 carries a handful of other changes that matter less to daily use but signal where engineering time is going. HDR (high dynamic range) video now plays on Windows once HDR mode is turned on in Windows’ own display settings, though laptops that only offer an “HDR video streaming” mode are not covered yet. JPEG XL, an image format built to beat JPEG, PNG, and WebP on compression, is available experimentally through Firefox Labs in the settings menu.

Right-clicking an open tab now generates a QR code for sharing that page offline, handy for printed materials where a clickable link does not help. On Linux, the same release quietly adds Vulkan video decoding support, a cross-vendor path around the aging VA-API system that has never had full NVIDIA backing.

Two changes tighten what other code can reach without asking first. Websites must now request permission before touching devices on a user’s home network, and extensions lose default access to local files, a permission Mozilla separated out from the broader “access your data for all websites” toggle.

153 is also the last release on Mozilla’s old monthly schedule. If the two-week cadence holds as planned, the next stable build lands in roughly a fortnight, the first real test of the faster pace.

Frequently Asked Questions

Does the PDF Merge Tool Work in Firefox on Android or iPhone?

The merge tool lives in the desktop PDF viewer’s sidebar. Firefox 153’s mobile changes are different: on Android, sharing a remote PDF now shares the file itself instead of just its web link, but there is no sign yet of the same drag-and-drop merge sidebar reaching phones.

Is Firefox 153 Available on Windows, Mac, and Linux Right Away?

Rollout is staggered. Windows and Mac users get it as an automatic update over the following few days, and Linux users should see it arrive through their distribution’s package repositories on a similar timeline.

How Do I Turn On JPEG XL Support in Firefox 153?

It is not on by default in the stable release. JPEG XL has to be switched on manually through Firefox Labs, where Mozilla groups its experimental, opt-in features inside the settings menu.

Is Firefox 153 Also an Extended Support Release?

Yes. Firefox 153 doubles as the newest Extended Support Release (ESR), the long-term branch Mozilla builds for enterprises and schools that need a stable version for months at a stretch rather than updating every few weeks.

When Does Mozilla’s Two-Week Release Schedule Actually Start?

With the version that follows 153. Mozilla has confirmed 153 is the final release on the old four-week cadence, though it has not published a fixed calendar for how the biweekly schedule will be dated going forward.