A "Pentium 4 or newer processor that supports SSE2" is recommended, not a strict requirement. The PC hardware requirements haven't changed since Firefox 4.0, released on March 22nd, 2011.

• http://www.mozilla.org/en-US/firefox/4.0/system-requirements/
• http://www.mozilla.org/firefox/system-requirements/

No plans to change that, as far as I can see.

• https://blog.mozilla.org/futurereleases/
• All 'SSE2' bug reports | Bugzilla

The only reference I can find to this change being proposed was around the time Firefox 4 was released. Given that it hasn't happened yet, and Firefox 29 is right around the corner, I'd say there's no need to worry about it in the immediate future.

• https://wiki.mozilla.org/Firefox/4/Platforms

Gingerbread Man, hi.

Thanks for replying and for your thoughts. Do you by any chance know whether or not certain features of Firefox are or will be unavailable to computers without SSE2 support even if certain updates, e.g. security updates, continue to be provided? One would hope that Mozilla/Firefox would give notice of this, but you never know.

I don't believe there's any difference in the feature set; it's just that without SSE2 performance suffers.

Others who happen to come across this thread should know that SSE2 was first introduced by Intel with the Pentium 4 back in 2001. AMD first added it back in 2003. The latest version of Windows won't even run without it.

• http://windows.microsoft.com/en-us/windows-8/what-is-pae-nx-sse2

In short, if you bought a computer in the last decade, its CPU probably supports SSE2. You can check using the CPU-Z utility.

• http://www.cpuid.com/cpuz.php

Thanks Gingerbread Man. Thankfully, so far, I have not noticed any deterioration in performance, but I am nevertheless aware of the limitations of my old laptop: it is, however, very well built, very reliable, which is part of the reason, besides money, I am loath to buy a new model.

Gingerbread Man, hi.

Can I just ask you one more question on this thread. I am now using FF 29.0.1, but I am concerned that if I update at this point I might get a version of FF that does not work on my computer and as a result I also lose access to all my bookmarks.

So, my question is, that if a new version of FF comes out that is not supported by my CPU (without SSE2 support) will Mozilla ensure that if I attempt to download it that it does not do so for reasons of incompatibility? (I have now, as a precaution, disabled automatic updates.)

Ian.F wrote:

I am now using FF 29.0.1, but I am concerned that if I update at this point I might get a version of FF that does not work on my computer

No need to worry. The current version is Firefox 30.0. I've tested Firefox 33.0a1 (2014-06-17) on a computer without an SSE2 processor and it works fine.

Ian.F wrote:

if a new version of FF comes out that is not supported by my CPU (without SSE2 support) will Mozilla ensure that if I attempt to download it that it does not do so for reasons of incompatibility?

Maybe. There are no plans to drop non-SSE2 support, so I can't say for sure how it would be handled. Again, the system requirements page and maybe the Future Releases Blog are the places to watch for any changes.

• http://www.mozilla.org/firefox/system-requirements/
• https://blog.mozilla.org/futurereleases/

Gingerbread Man, hi.

Thanks for replying: what you say helps.

As you may know, Google Chrome has started sending out messages to computers with non-SSE2-supported CPU's noting that the user's computer hardware is no longer supported and soon will no longer receive updates, so to this extent I would not have to worry that an incompatible version of that browser will be downloaded to replace the existing usable one (I only actually use Chrome for testing purposes so I am not too concerned there anyway). I was hoping that FF might adopt the same straight-forward approach. For now I will update to FF30.0. Many thanks.