It appears that Mozilla Foundation is trying to discourage the use of the Thunderbird email client. The newest version of Thunderbird, 31.2.0, has the Save-As bug. All file saves are Save As, and suggest a different file name than saved before.
Other obvious bugs were introduced. For example, the fields for email addresses are much more difficult to read. The Save-As bug has been reported, but no new version has been released.
If many windows and tabs are open for a long time, Firefox now crashes in a way that does not cause a crash report to be sent.