nsHTMLDocument::CreateElementNS

Hi,

We are looking to DOM/JS related issues in Firefox. One problem that's 
been perplexing us is as follows: We are running the same version of 
Firefox with the same set of modifications (synchronizing with 
Mercurial) and same OS (Fedora 10 x86_64), but we always get different 
execution flows around the function nsHTMLDocument::CreateElementNS. Two 
of our machines execute the above function each time it is browsing any 
web page, the rest of our machines never touch that function, according 
to gdb breakpoints and logging information hooked into the source code 
of that function.
Can anyone tell us why it is get call on some machine and not on others, 
Even though they are having same software configuration?