This bug was disovered by m_mozilla@wickline.org in bug 70054. It is seen on all current builds of Mozilla on Windows, Linux, and Mac. Just load http://peds.wustl.edu/div/gi/spec/tpn/tpn_calculator.html, enter the javascript:URL below, and you will get a timing result. For convenience, the javascript:URL to use is saved at http://bugzilla.mozilla.org/showattachment.cgi?attach_id=72417 It contains: javascript: var frm=document.tpncalc; void(frm.raw_age.value='3'); set_age_number(); void(frm.weight_kg.value = '4'); set_weight(); void(frm.height_cm.value = '56'); set_height(); var start = new Date(); calc_group_1_run(); var end = new Date(); alert(end - start); The effect is to take the three data values for age, weight, and height and calculate the correct values for the remaining textboxes on the page. This is done in a cascading manner (the values for Group 1 determine the values for Group 2, which determine... etc.) Here are my results on WinNT (128M RAM, 500MHz processor) (My Mozilla build was 20020222xx; all times in milliseconds): NN4.7 IE6 Mozilla 16 200 900 m_mozilla@wickline.org got these results: NN 4.78 on OS X via classic 25 MSIE 5.1 on OS X 8106 Mozilla build 2002030403 on OS X 4228 We discussed these results in bug 70054, and felt that the problem here is not with JS Engine but with DHTML. The fast time for NN4.7 is strong evidence for this, since AFAIK the performance of JS Engine has not degraded from version 1.4 to the current version 1.5; and if anything, has gotten faster.

cc'ing Fabian to see whether this is a duplicate of, or a dependency for, the DHTML performance tracking bug 21762 -

Adding dependency

http://bugzilla.mozilla.org/show_bug.cgi?id=70054#12 as indicated in the above comment, this was fixed with the fix in bug 129115 -matt *** This bug has been marked as a duplicate of 129115 ***