Firefox Portable 14.01 takes long time to load, timeout on scripts

I have never had this problem before except for the last few weeks when I updated firefox. Even clean installations have this error (without extensions or plugins)

When opening pages with have some javascript content, Firefox takes a long time to load the page (about:home, loads immediately). I even get errors like script taking too long to load etc on educational pages. This did not happen with the older versions. The initial load happens and then firefox does not respond for a long time.

However, browsers like Google Chrome and Explorer have no problems opening the page and do so at the same time. I am done browsing with the page and firefox has still not loaded the page completely and is not responding.

Can anyone offer any suggestions?

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I have since updated to Firefox 15.0 and still have the same problem. Following the advice of a colleague, I disabled the add-ons one at a time (probably brought over from the rest of my installation). I have found the culprit to be Shockwave Flash. If I disable this, then the loading seems to be faster.
You can check with the following websites
www.sp.edu.sg
www.jetstar.com
The message is xxXXXxxXXXXx.js is taking too long to execute.