OK,
First of all, the function is loaded from *.js file.
Then it is called 6 or 7 times on one page by call like this:
loadJSintoDIV('emailsList', 'crm_overview_emails.php?unique=emailsList&thr_id={$thr_id}&kon_id={$kon_id}&List_Eml_ID={$get.List_Eml_ID}', true); //code in {...} is Smarty
Now, first load of page. If the last parameter is true, div is still hidden. If false, div is loaded by appendChild(). Of course, later every part of page can be hidden and loaded by button, but it is working.
The problem is, that while page is loading 3 functions have last parameter false, so 3 parts normally was loaded. After last FF update only first is loaded, and other 2 is not.
Starting to work with alert, as i said...
Any ideas?