You can download Firefox 52.9.0 ESR from the official Mozilla FTP archive
The primary reason this version remains a sought-after download is the death of legacy extensions. For over a decade, Firefox’s superpower was its add-on ecosystem. Unlike Chrome’s stricter, sandboxed extensions, Firefox allowed deep, system-level modifications. Powerful tools like DownThemAll , Classic Theme Restorer , and intricate privacy scripts could alter the very soul of the browser. However, Mozilla eventually decided that this power came at the cost of security and performance, specifically regarding the implementation of multi-process architecture (Electrolysis) to prevent browser crashes. firefox version 52.9. 0 esr download