Firefox 3.1: How to Enable the TraceMonkey JavaScript Engine

TraceMonkey is the magic pill that makes the new Firefox much quicker. Unfortunately, the beta version has this feature disabled. By changing the value of a couple of configuration settings, you can easily enable TraceMonkey and enjoy its speedy goodness.

1. Open Firefox.

2. In the Location Bar, input about:config.

3. Click to get past the warning message that appears.

4. Locate the Preference Name

5. Double-click the preference and change the value to true.

6. Locate the Preference Name javascript.options.jit.content.

7. Double-click the preference and change the value to true.


About Rob Rogers

Once a prolific author here on Tech-Recipes, Rob has moved on to greener pastures.
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19 Responses to “Firefox 3.1: How to Enable the TraceMonkey JavaScript Engine”

  1. October 16, 2008 at 1:51 am, fastfreddie1959 said:

    Locate the Preference Name
    Locate the Preference Name javascript.options.jit.content.

    Neither key exsists in FF 3.1


    • October 16, 2008 at 2:51 am, Rob Rogers said:

      Actually, they do. Go to about:config and input the word javascript into the filter. They will be the 4th and 5th preferences listed.


      • October 18, 2008 at 4:31 pm, pearlworm said:

        Locate the Preference Name
        Locate the Preference Name javascript.options.jit.content.

        Nope! still not in my version 3.03


        • December 10, 2008 at 6:03 pm, nanda said:

          they won’t be in 3.03, this is about 3.1


    • October 21, 2008 at 5:31 am, adi said:

      its a tweak for firefox Minefield, not 3.03


  2. October 18, 2008 at 4:41 pm, pearlworm said:

    Okay, downloaded Minefield and found them Thanks


    • October 20, 2008 at 3:27 am, caffino said:

      how do you download minefield
      i looked and nothing showed up


      • October 30, 2008 at 3:03 pm, kansei said:

        it’s called google. Try “download minefield” it’s all over the first results


  3. October 19, 2008 at 11:07 pm, Geoff said:

    Fantabulous feature! Tnx a $M


  4. November 04, 2008 at 8:47 am, dorai said:

    it is good i done it very easily


  5. November 08, 2008 at 1:31 pm, Trikkk said:

    do you have any technical details or an link about how is this change of speed happening ? I mean, I have enabled both options(the truth is that in 3.1b2pre —– Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.9.1b2pre) Gecko/20081107 Minefield/3.1b2pre, the option:’javascript.options.jit.content.’ is already enabled by default, so just enabled the “….chrome” .I have already seen an important increase at speed, but I need to know how it is achieved.I mean, where’s the catch?


    • December 04, 2008 at 1:57 am, Kris said:

      Google JIT or Tracemonkey

      There is no catch


  6. December 05, 2008 at 9:45 pm, Mallikarjun said:

    FF is not troubling me now ………….Thanks


  7. December 09, 2008 at 1:34 am, Ross said:

    Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2a1pre) Gecko/20081208 Minefield/3.2a1pre

    This doesn’t seem to make a difference for me, tested using sunspider javascript benchmark.


  8. February 20, 2009 at 2:46 pm, nagu said:

    8. If things break, remember what you did in #3.


  9. February 20, 2009 at 2:47 pm, nagu said:

    Minefield Rocks!


  10. July 12, 2009 at 11:25 pm, Anonymous said:

    OMG! Thank you for the information. It worked GREAT!


  11. October 07, 2009 at 5:18 am, Anonymous said:

    i could not find following in about:config.



  12. March 04, 2010 at 10:00 am, Travel Trailers said:

    now i know, i thought i will nver get through it… thanks…


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