When I click edit/preferences/advanced, I get an error:
XML parsing error: not well-formed. Location: chrome://messenger/content/pref-advance.xul Line 208, column 5
----^
hmmm, composing this I discovered another bug... if I place the cursor on the text lines above, and press the "end" key, the cursor moves to the end of the line. (expected)
When I put the cursor on the ----^ line and press the "end" key, the cursor moves to the *beginning* of the line... not expected.
I went to bugzilla the end-key problem, and discovered the same problem in the bugzilla reporting area.... so that told me it was not a thunderbird problem... so I canceled my bug report.
(the xml parsing error IS submitted as Filed as: https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=151977 )