Hi there, is there anything what could be tweaked in about:config to resolve below issue? Proxy Pac file used, pac file is quite long but doesn't create issue in general. Now, occasionally some web application cannot open at all. It is happening only in Firefox and not other browsers. I narrow down that it must be related to some timers because if explicit rule in Pac file to send proxy is put somewhere near top, it works. Pac doesn't have to be processed until last default rule. Or it can be resolved by reducing number of dns suffixes I think there was 7 when I was removing them then on count 4 page started loading. Thank you Lukas