Dear Maintainer,

   * What led up to the situation?

imap server certificate was replaced with new one (self-signed)

   * What exactly did you do (or not do) that was effective (or
     ineffective)?

icedove was running some time without being used, trying to fetch new messages.
Every attempt caused new request to confirm certificate acceptance.
Subsequent requests were not cancelled after first (with accept permanently).

   * What was the outcome of this action?

Modal dialog window blocks application and every "accept" or "cancel" just
started those "fancy" gnome close- and open-window animations.
With modal, application was blocked. I had to press button (ok, ESC works too
but that's irrelevant) on every dialog even that certificate was already
accepted.

   * What outcome did you expect instead?

Show this dialog only once, in this case probably cancel fetch attempt is
request for user action with same parameters is already started. Probably also
cancel started request(s) if it becomes invalid (eg: two certificate changes -
invalidate first request and replace it with new, if necessary)