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Mozilla today launched Firefox 77 for Windows, Mac, and Linux. Firefox 77 includes faster JavaScript debugging, optional permissions for extensions, and Pocket recommendations in the U.K. You can download Firefox 77 for desktop now from, and all existing users should be able to upgrade to it automatically. According to Mozilla, Firefox has about 250 million active users, making it a major platform for web developers to consider.

Everyone is spending more time in their browsers as they learn and work from home, but software developers building the browsers have also been disrupted. Google and Microsoft had to adjust their respective browser release schedules due to the coronavirus pandemic. In April, however, Mozilla said that while “some of our competitors have had to slow down or stop work,” it is sticking with its 2020 Firefox release schedule.

Firefox 77 is thus arriving right on time as part of the browser’s four-week release cadence. While the schedule remains unchanged, Mozilla shifted its roadmap to avoid shipping changes that might negatively impact the user experience on, or possibly break, government and health services websites. That may be why Firefox 77 isn’t as hefty as previous versions.

Developer features

Other than Pocket recommendations arriving in the U.K. (they’ve been in Canada, Germany, and the U.S. since April 2018), this is primarily a developer release.


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Firefox’s Debugger is now better at handling large web apps with all their bundling, live reloading, and dependencies. Mozilla is promising performance improvements that speed up pausing and stepping, as well as cutting down on memory usage over time. Source maps should also see performance boosts — some inline source maps load 10 times faster — and improved reliability for many configurations. The debugger will now also respect the currently selected stack when stepping, which is useful when you’ve stepped into a function call or paused in a library method further down in the stack.

Ever since Firefox Quantum arrived in November 2017, Firefox users have been prompted when an extension wants certain permissions. That primarily happens during installation or when new permissions are added during an extension update. Users sometimes reject these permission requests during an extension’s update, which leaves them on an old version. In Firefox 77, extension developers can make more permissions available as optional permissions, which don’t trigger a permission request upon installation or an extension update. Optional permissions can also be requested at runtime so users see what permissions are being requested in context.

Firefox 77 also brings a new settings menu for Network and Debugger, a new watchpoints option that combines get/set, and improved Network data preview. New web platform features include String#replaceAll for replacing all occurrences of a string and IndexedDB cursor requests. If you’re a web developer, check out the details here: Firefox 77 for developers.

Windows, Mac, and Linux

There are a few other additions in this release. Here’s the full Firefox 77 for desktop changelog:

  • Pocket recommendations will appear on the Firefox new tab for our users in the U.K. If you don’t see them, you can turn on Pocket articles in your new tab, follow these steps.
  • WebRender continues its rollout to more Firefox for Windows users, now available by default on Windows 10 laptops running on Nvidia GPUs with medium (<= 3440×1440) and large screens (> 3440×1440).
  • You can view and manage web certificates more easily on the new about:certificate page.
  • Significant improvements to JavaScript debugging make loading and stepping through sources faster and with less memory being used over time. Source map support also got a lot more reliable and will just work for a lot more cases.
  • Added support for the JavaScript API String.prototype.replaceAll(), which allows developers to return a new string with all matches to the provided pattern while preserving the original string.
  • The browser.urlbar.oneOffSearches preference has been removed. To hide one-off search buttons, uncheck search engines on the about:preferences#search page.
  • Various <a href=”” security fixes.
  • The applications list in Firefox Options is now accessible to screen reader users.
  • Some live regions previously didn’t report updated text with the JAWS screen reader. This issue has been fixed.
  • Date/time inputs are now no longer missing labels for users of accessibility tools.

Mozilla is still working on Firefox Preview, a new version of Firefox for Android powered by GeckoView. Mozilla plans to launch the new Firefox for Android in the first half of 2020 — it’s got less than a month left.

Mozilla releases new Firefox versions every four weeks. Firefox 78 is currently slated for July.

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