User Agent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:34.0) Gecko/20100101 Firefox/34.0 Build ID: 20141127111021 Steps to reproduce: This is an "improvement suggestion" I routinely move large (several thousand) emails between IMAP folders - which takes minutes. During such moves, TB will report: Unresponsive script warning... A script on this page may be busy Script: chrome://messenger/content/folderPane.js:2061 Totally understandable. You probably have some kind of watchdog looking for hung processes and when this particular one doesn't return in XX seconds, you ask the user to make a decision. I just click on "continue"/whatever and it carries on to successfully carry out the operation Well that is understandable for you and I, but it's not understandable for our Mums and Dads :-) Basically you are exposing a raw programming warning to end users - which 99.9% of humanity do not understand (that won't be an exaggeration), nor can they make logical decisions over what to do next. Can that "XX secs" be changed based on new information? Could TB notice it had 100+ messages to move, and so increases the watchdog timeout x10 until it's finished? I think having that watchdog changed based on better understanding of slow operations would improve the user experience Thanks for listening! Jason

Thanks for the report. It's basically a performance issue that's probably already covered in a couple other bug reports. A couple are being worked on. Someone will probably eventually match it up.

How many messages in the source and target folder?