Mozilla officially announced the release of Firefox 155 , marking the start of its new bi-weekly release cycle. This change will allow the organization to roll out new features more frequently, stabilize the development workflow, and reduce the engineering team's workload before each release.
Mozilla has patched a total of 109 vulnerabilities in this release, the vast majority of which were related to memory management flaws, specifically buffer overflows and use-after-free vulnerabilities.
Main new features of Firefox 155
In this new version of Firefox 155, one of its most important new features can be found in the user experience: the deployment of "Smart Window" mode, currently enabled for users in the United States, Canada, and France.
This environment complements standard and private browsing by offering a dedicated space for interacting with artificial intelligence. Key features include personalized suggestions for resuming previous conversations, automatic tab grouping with AI-generated descriptive names, and significantly faster citation of web sources using the exa.ai search engine.
Regarding privacy and security, the address bar has been updated to display a visual counter of blocked trackers next to the shield icon. This feature is being rolled out gradually, but you can force its activation by modifying the `browser.urlbar.trackerCount.featureGate` parameter in ` about:config`.
On the other hand, to prevent unwanted executions, the browser will no longer process mailto: links automatically, so explicit user interaction is now required to open the email client.
The organization of the workspace is also improved: the native settings now allow you to freely reorder the list of containers . Furthermore, when printing PDF documents whose content is smaller than the paper, the system will automatically adjust the scale to fill the entire printed page.
Developer Tools
The Elements inspector, the options to emulate CSS features, have been moved to a new panel accessible via the "@ " button in the Rules tab, where it is now possible to emulate the prefers-reduced-motion query.
The JavaScript debugger boosts productivity with the new Ctrl+Alt+B shortcut, which toggles all breakpoints at once. Additionally, the built-in JSON viewer can now interpret and display documents in JSON Lines (JSONL and NDJSON) format.
The rendering engine expands its compatibility with modern CSS specifications. The mathematical function `progress()` is implemented to calculate relative positions between a minimum and a maximum, and the `alpha()` function is implemented to directly modify the transparency of a specific color.
The `attr()` function has been improved, now allowing it to work with HTML attribute values ​​of any type, not just text strings. The `font-width` property has also been added as a standard equivalent to `font-stretch`. As a safeguard against renderer crashes, the engine now limits the nesting of CSS blocks and functions to a maximum of 75 levels.
At the JavaScript level, support is added for the Promise.allKeyed and Promise.allSettledKeyed methods , operating on objects instead of arrays to simplify promise management. WebAssembly receives weight optimizations by supporting the compact binary format extension (reducing the size of modules with many imports) and adding 128-bit arithmetic instructions for high-precision operations.
Network communications are also evolving : the second version of the QUIC protocol is enabled for HTTP/3 connections , and the WebTransport API adds support for send groups (createSendGroup), datagrams, and TLS session-linked key generation. As a technical note for network administrators, the domain for detecting captive portals has officially changed to firefox-portal-detection.com.
Android Optimizations
The Android mobile version now allows users to directly activate edit mode by pressing and holding any toolbar button, simplifies the process for deleting tabs within a group , and improves the sensitivity of the page summary feature when the phone is shaken. On Windows desktops, users who use the browser for gaming benefit from full support for Nintendo Switch Pro controllers, with accurate mapping of the analog sticks and directional pad.
Finally, if you are interested in learning more, you can find the details at the following link.
How to install or update to Firefox 155
If you already have Firefox installed, the update should arrive automatically through your distribution's package manager in the next few days. However, if you want to get version 155 immediately without waiting for the official repositories , the best option is to use the official binary provided by Mozilla.
To install it from the binary on any Linux distribution (Ubuntu, Fedora, Arch, etc.), you can follow these steps in your terminal:
wget -O firefox.tar.bz2 "https://download.mozilla.org/?product=firefox-latest&os=linux64&lang=es-ES" sudo tar xjf firefox.tar.bz2 -C /opt/ sudo ln -sf /opt/firefox/firefox /usr/bin/firefox
If you prefer to use Snap packages (common in Ubuntu), you can force the update with:
Sudo Snap Refresh Firefox
For users who prefer Flatpak and Flathub, the update can be performed by running:
flatpak update org.mozilla.firefox
For users of Ubuntu, Linux Mint, and other Ubuntu derivatives, it's also possible to update Firefox via the official PPA . To do so, open a terminal and enter the following commands:
sudo add-apt-repository ppa:ubuntu-mozilla-security/ppa -y sudo apt-get update sudo apt install firefox
Finally, if you prefer to wait for it to arrive in your distribution's native repositories (DNF, Pacman), you just need to run your system's usual update command, although keep in mind that this can take anywhere from a few hours (on Arch) to several days (on Debian/Ubuntu).