64 Bit Firefox 4

Start Firefox 4 in 32-bit Mode For Less RAM Usage

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64 Bit Firefox 4
64 Bit Firefox 4

If you hadn’t noticed yet, Firefox 4 now runs in 64-bit mode by default (at least on Mac anyway). I’ve noticed that Firefox uses up almost double the ram in 64-bit mode compared to when running in 32-bit mode. Also, some plugins (like Silverlight) are not yet compatible with the 64-bit mode of Firefox.


Update: running in 32-bit mode will also help with a known problem with Java MIME types not being recognized correctly.

Here’s how to run Firefox 4 in 32-bit mode (by default) on Mac OS X:

  1. Using Finder, navigate to your Applications folder and locate the Firefox app.
  2. Command+Click (or Right-Click if you have a 2+ button mouse) and go to: “Get Info”.
  3. Check the box that says: “Open in 32-bit Mode” and close the Firefox Info box.
  4. Quit and then Relaunch Firefox.
Open Firefox 4 in 32 Bit Mode
Open Firefox 4 in 32 Bit Mode (click to enlarge)

It’s as easy as that!

Note that 64-bit Firefox does run faster than 32-bit Firefox, but you probably wont notice that much of a difference, and you will reap the benefit of less memory usage, which can be crucial if your system is always low on RAM.
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Alex is a professional web and mobile developer. He loves spending time with his wife and kids, and is still very much a kid at heart. He enjoys reading comic books, watching TV/Movies, playing video games, playing with action figures and Legos.

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9 thoughts on “Start Firefox 4 in 32-bit Mode For Less RAM Usage”

  1. Thanks Alex,

    I just installed Firefox 4 yesterday hoping the update would address the RAM-munching problems of FF 3, but to my chagrin I noticed that FF 4 quickly ramped up using over 1GB of RAM!

    Thanks for your tip. This seems to keep things at least at FF 3 levels (using ~400 MB on my Mac Pro system with 3GB of RAM).

    1. You’re welcome Pete!

      Thanks for your comment. I know what you mean as I have had the same problems. I’m glad this worked for you too. It would be nice if there was a way to tame down the 400+MB usage, but everything I’ve read seems to indicate it’s a plugin/addon problem. Though I have found that If I avoid using websites heavy in Flash (like Youtube) it keeps the usage down a lot better.

  2. i have done these steps, but on pages using adobe flash i still always get the message that it needs to be restarted in 32 bit mode. is there a way to check what mode it’s in while running the application?

    1. hmm… that is odd… Well one way you can check is by opening your Activity Monitor (Applications->Utilities->Activity Monitor) and look for Firefox on the left (note: you can sort by a category if you click on the column heading, click again to change from ascending to descending) when you find Firefox, look to the right under “Kind” and it will either say “Intel” (which is 32-bit mode) or “Intel (64 bit)”.

  3. I’m running OS X 10.6.7 – Firefox 4.0.1 – Safari 5.0.5 and am trying to run 32 bit rate. I’ve gone to get info (both directly and thru above steps) and neither browser offers the “run in 32 bit mode” option. Firefox only offers “Locked” and Safari offers “Open using Rosetta” and “Locked” Am i doing something wrong? (all fields in “Get Info” are titlted open to see all contents)

  4. First of all I would like to say awesome blog! I had a quick question in which I’d like to ask if you do not mind. I was interested to find out how you center yourself and clear your mind before writing. I have had a difficult time clearing my mind in getting my thoughts out. I do enjoy writing however it just seems like the first 10 to 15 minutes are wasted just trying to figure out how to begin. Any suggestions or hints? Kudos!|

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