Take the 2-minute tour ×
Ask Ubuntu is a question and answer site for Ubuntu users and developers. It's 100% free, no registration required.

I have a 64 bit Ubuntu. For the preinstalled Firefox i had to download the 64 bit plugins (flash, java), the 32 bit plugins didn't work. Then I downloaded Firefox from mozilla.org, which just has one version to download and it does not state whether it is 32 bit or 64 bit. Using this downloaded Firefox all the 64 bit plugins no longer work. I had to download the 32 bit plugins.

How can I tell whether my Firefox is 32 bit or 64 bit?

share|improve this question
add comment

5 Answers 5

up vote 13 down vote accepted

Just open firefox and type about: in the address bar. You will get the about Firefox page. At the bottom you can see the 'Build identifier' information this will tell you about architecture.

If it is 32-bit you will get something like this:

Build identifier: Mozilla/5.0 (X11; U; Linux i686; en-US; rv: Gecko/20101027 Ubuntu/10.10 (maverick) Firefox/3.6.12

Note: i686, i386, i586 are 32-bit builds.

If it is 64-bit you will get something like:

Build identifier: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv: Gecko/20101027 Ubuntu/10.10 (maverick) Firefox/3.6.12

share|improve this answer
Complementing the info above, if you are on a 32bit Firefox running on 64bit system, then you will see (X11;U;Linux i686 on x86_64...). Additionally, Firefox 4 has now a about:support page that gives that information, plus other useful ones. –  lovinglinux Nov 2 '10 at 14:28
@lovinglinux: You are right i missed that point.. –  aneeshep Nov 2 '10 at 14:32
add comment

From command line, run:

file /usr/lib/firefox-*/firefox-bin

It will tell you whether the binary executable is 32 or 64-bit.

With newer versions of Firefox, you'll need to run:

file /usr/lib/firefox*/firefox
share|improve this answer
add comment



At the "Build platform's target" you should see something like this:

share|improve this answer
add comment

on firefox > help > about mozilla firefox

Mozilla/5.0 (X11; U; Linux x86_64; ...

share|improve this answer
Doesn't work with newer versions. –  Eric Carvalho Dec 27 '12 at 1:19
add comment

You can get even more information with:


It's got a lot more technical information compared to "about:buildconfig". As when I was trying to troubleshoot an issue regarding 64bit it helped me more then the other thing did.

share|improve this answer
add comment

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.