Created attachment 8742002 [details] Thunderbird bug.ogv User Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Firefox/45.0 Build ID: 20160319124722 Steps to reproduce: I copied and pasted a text from PDF file into the message edition window. Then I deleted the quotation mark and new line from it. My thunderbird version is 38.7.0-1, I'm using 64-bit manjaro linux. Actual results: Some CSS style showed up, you can see the results on that video: https://www.youtube.com/watch?v=ZgDm4vYXB98 (it's attached to this bug as well). Expected results: Characters should be deleted instead of entered.
Created attachment 8742003 [details] File that I copied contents from Wops, it was a doc file actually, not a PDF. Sorry for that mistake.
Many people think that Thunderbird has control over the editing of the mail body. This is not the case. All the editing happens in the Mozilla core module "Editor". So this is not a Thunderbird problem but an M-C editor problem. And, BTW, the M-C editor is an unowned module, so no bug fixes can be expected.
(64bit is used to indicate problem happens *only* in 64bit environment - not likely the case here)