Hello, Can you please confirm that the issue you are facing is that Firefox froze when you were on a particular site. Is that the issue you are facing ? If so, can you please share the details of the website so that we can check if there is a long-running script on it.

Warning Unresponsive script - What it means and how to fix it

Thank You

Sorry. that tab is closed & I can't re-create it. All I want is to go from mbox to maildir on two accounts years old. Thanx anyway, bob

So what user name did you use to ask your previous question. This is the only one I can find. Or had you old gone so far as to be offered similar responses to your question by the forum software?

Based on your last response I would assume this should provide the answers you need. https://support.mozilla.org/en-US/kb/maildir-thunderbird

It is a simple process, but still not a mainstream activity due to bugs causing data loss that are unresolved.