For many, this version was a "time capsule." It was one of the last versions to support older operating systems like Windows XP and Vista reliably. It also maintained compatibility with "Legacy" add-ons—those classic extensions that changed the look and feel of the browser before Firefox moved to the modern WebExtensions system. A Note for Today
Version 45 completely retired the built-in Tab Groups feature. Mozilla removed it because telemetry showed very low overall user engagement. This change optimized system resources but forced dedicated power users to migrate to external extensions for workspace organization. Developer Tool Overhaul mozilla firefox 450 1 old version
Installing an older version of Firefox will not automatically erase your bookmarks, history, or passwords, but a profile created in 2026 may be corrupted or made unusable by a version from 2016. It is highly recommended to use a separate, fresh Firefox profile for testing. For many, this version was a "time capsule