Is this about future support for the old EOL Windows XP ? or about needing a CPU that supports SSE2 ? Mozilla is looking drop WinXP support as of Firefox''' 53'''.0 and later. This was not a matter of if but when as It is getting harder for Mozilla to deal with issues and testing on WinXP now days along with the costs. If this happens then in order to have Firefox security updates for a while still you can use the then Firefox 52.0 ESR as the updates are for security and allowed stability fixes. A version on the ESR channel generally gets eight updates (unless Mozilla extends support) so 52.8.0esr will be out when Firefox 60 is Released. https://www.mozilla.org/firefox/organizations/faq/ A tracking bug on this is "[https://bugzilla.mozilla.org/show_bug.cgi?id=1130266 Bug 1130266] - (xp-eol) Drop support for Windows XP/Vista" however l the Bugzilla issues tracker is not a discussion forum like here [https://bugzilla.mozilla.org/page.cgi?id=etiquette.htm Bugzilla etiquette]. Mozilla has already supported Windows XP and Vista months longer than other browsers as Chrome dropped WinXP/Vista back in April as of Chrome 50 and [http://www.ghacks.net/2016/02/17/opera-36-will-be-the-last-for-windows-xp-and-vista/ Opera 36 was the last that supported WinXP/Vista]. https://www.mozilla.org/firefox/49.0/releasenotes/ <blockquote>Ended Firefox for Windows support for SSE processors</blockquote> SSE2 has been mentioned as a requirement since the [https://www.mozilla.org/en-US/firefox/4.0/system-requirements/ Firefox 4.0 (four.zero) System Requirements] however it was still possible to get away with running Firefox on older CPU's that did not support SSE2 up til 48.0. The only supported Firefox version that will still work on older CPU's without SSE2 support is the Firefox 45 ESR as the current version is [https://www.mozilla.org/en-US/firefox/organizations/faq/ Firefox45.5.0esr] which was released at same tome as Firefox 50.0 Release. SSE2 support has been in CPU's since 2001 for Intel or 2003 for AMD depending. https://en.wikipedia.org/wiki/SSE2 ---- Note I do not work for Mozilla so I would appreciate if you refrain from insults or language if this does not answer the brief question you posted.