Mainstream browsers have long since stopped supporting Windows 7, 8, and 8.1, but there's one browser that refuses to abandon these dead versions of Windows. Mozilla continues to release security updates for Firefox 115 ESR on unsupported versions of Windows, and they have no plans to stop anytime soon.
In early 2023, Mozilla announced plans to end Firefox updates on Windows 7 in September 2024. However, when September 2024 rolled around, Mozilla decided to continue Firefox 115 ESR updates for another six months, citing that there were still enough Firefox users on Windows 7 to justify the extended support. Firefox will now receive another half-year of security updates.

According to the official release schedule, Firefox 115 ESR will continue to receive updates until September 2025. The extended support policy may even be extended further, as Mozilla has stated that it will reevaluate this decision in August 2025:
We have decided to extend support for ESR 115 on Windows 7-8.1 and macOS 10.12-10.14 only until September 2025. We will re-evaluate this decision in August 2025 and communicate any updates regarding the end of support for ESR 115 at that time.
Note that these changes only apply to Windows 7, Windows 8, Windows 8.1, and macOS 10.12, 10.13, and 10.14. Firefox users on more modern, supported operating systems can move to newer versions. Currently, Mozilla offers version 135 on the regular release channel and version 128 on the Extended Support Release (ESR) channel. You can download Firefox ESR from the official website.
Mozilla originally planned to end support for Windows 7-8.1 in September 2024, but changed plans. Mozilla now provides two ESR releases: 115 for unsupported operating systems, and 128 for Windows 10 and later. Removing Windows 7 support from Firefox 116 and later allows Mozilla to clean up the codebase and remove the burden of maintaining newer libraries that no longer support pre-Windows 10 releases.
But on the other hand, Firefox still has "a lot of users on Windows 7, and the Windows 7 market share itself is still quite large. Therefore, how long to maintain updates is something Mozilla needs to consider carefully. According to a comment from a Firefox engineer, Mozilla "hopes to have more official announcements on this issue in the near future".
For reference, Microsoft, Google, and other browsers have stopped supporting their browsers on versions of Windows prior to Windows 10 since January 2023. Chromium's end of support on Windows 7, 8, and 8.1 has forced other developers, such as Valve and Steam, to stop updating their software as well.
In reality, running an unsupported browser on a version of Windows that’s already dead isn’t all that scary. There are still plenty of people using Windows XP in 2022. But accessing the modern internet with software that no longer receives security updates isn’t a good idea. Those who choose to stick with Windows 7 should be prepared to say goodbye to their beloved operating system and move to a supported operating system with longer-term supported browsers.