If your computer has a processor older than Pentium 4, Firefox is no longer supported as of version 49.
If Firefox is already installed on your computer, you can continue using it but you will not receive updates beyond version 48. If you download Firefox version 49 or above and try to install it, you will see the message, Firefox cannot be installed. This version of Firefox requires a processor with SSE2 support.
Firefox Extended Support Release (ESR) version 45 will continue to work with older processors but is no longer being updated. Firefox ESR version 52, released March 7, 2017, is not supported.
Like many programs, newer versions of Firefox require a processor that supports Streaming SIMD Extensions 2 (SSE2) for better security and performance. We recommend a computer with a Pentium 4 or newer processor that supports SSE2 to use the latest version of Firefox, which has more features, stability and security.
If your computer has a processor older than Pentium 4, Firefox is no longer supported as of version 53.
If Firefox is already installed on your computer, you can continue using it but you will not receive updates beyond version 52. If you download Firefox version 53 or above and try to run it, you will see the message in stderr, This browser version requires a processor with the SSE2 instruction set extension. You may be able to obtain a version that does not require SSE2 from your Linux distribution.
Like many programs, newer versions of Firefox require a processor that supports Streaming SIMD Extensions 2 (SSE2) for better performance. We recommend a computer with a Pentium 4 or newer processor that supports SSE2 to use the latest version of Firefox, which has more features, stability and security.
Firefox Extended Support Release (ESR) will continue to work with older processors but will not receive updates beyond ESR version 52. Firefox ESR version 60, released May 9, 2018, is not supported.
The processor requirements of Firefox as distributed by Linux distributions may differ from the processor requirements of Firefox as distributed by Mozilla, so you may be able to obtain an up-to-date version of Firefox that does not require SSE2 from your Linux distribution.
