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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?

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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:1.9.2.12) 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:1.9.2.12) Gecko/20101027 Ubuntu/10.10 (maverick) Firefox/3.6.12

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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
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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
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visit

about:buildconfig

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

x86_64-pc-linux-gnu"
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on firefox > help > about mozilla firefox

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

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Doesn't work with newer versions. –  Eric Carvalho Dec 27 '12 at 1:19
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You can get even more information with:

about:support

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.

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