Steps how to reproduce with with English SeaMonkey 2.41a1 (X11; Linux x86_64; rv:44.0) Gecko/20100101 Firefox/44.0 Build 20151103003001 (Classic Theme) on VirtualBox Ubuntu 14.04 LTS: 0. Create VirtualBox 64Bit Ubuntu 14.04 LTS if you do not have a 64bit Linux/Ubuntu machine → if necessary install Firefox and Thunderbird, make them default applications for everything they ask for. 1. Install above mentioned SeaMonkey 64bit 2. Launch SM, confirm all checkboxes "Make SM Standard appliction", uncheck "Always Ask" → [ok] 3. Quit SM → Relaunch SM → Menu 'Edit → Preferences → Mail & Newgroups → Make SM Default application for Mail, News, Feeds' (Strange, after step 2 all 3 buttons should have been greyed) → [Close] 4. Redo Step 3: Bug: Mail, News, Feeds not greyed, it seems that step 3 did not make SM Mail default application as expected. Some more tests: 5. Try to send an ODF (OpenOffice) document as PDF via e-mail From AOO/LibO via file menu expected: SM opens, Mail Composer opens new mail with PDF attachment actual: Thunderbird will be opened with PDF as attachment One more test: 6. In Linux folder Personal/Documents/Downloads rightclick an arbitrary file (I used "seamonkey-2.41a1.en-US.linux-x86_64.tar.bz2") → Email... → Send as:Email → add recipient adress → [Send] Expected: SM e-mail client opens with file as attachment Bug: TB opens with file as attachment One more test: 7. To a LibO Writer document add a word with mailto: link behind it 8. <control+click> on word with mailto-link Expected: SM e-mail client opens Bug: TB opens Additional information: a) I can't tell whether this is 64bit related (like Bug 1175598), I currently only have 64Bit machine b) OS Integration or MailCore, that is the question here.
c) No Linux related DUPs found with <https://bugzilla.mozilla.org/buglist.cgi?cmdtype=dorem&remaction=run&namedcmd=DUPs1226839&sharer_id=41036>
d) Also REPRODUCIBLE with SeaMonkey 2.42a1 Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:45.0) from ~akalla/unofficial/) Gecko/20100101 Firefox/ 45.0 Build 20160308135604, (Default Classic Theme) on German WIN7 64bit e) REPRODUCIBLE with unofficial (from <http://seamonkey.callek.net/contrib/>) en-US SeaMonkey 2.44a1 Mozilla/5.0 (Windows NT 6.1; x64; rv:47.0) Gecko/20100101 Firefox/47.0 Build 20160208090255 (Default Classic Theme) on German WIN7 64bit e) Works fine with all my other SM versions installed on my PC: 2.35, 2.38, 2.39 (all 32 bit) I need to test a 32 Bit Version.
f) NOT reproducible with SeaMonkey 2.42a1 Mozilla/5.0 (Windows NT 6.1; WOW64; rv:45.0) from ~akalla/unofficial/) Gecko/20100101 Firefox/ 45.0 Build 20160308183715, (Default Classic Theme) on German WIN7 64bit e): Now I am pretty sure that it's a 64Bit problem. g) I did not test "Default news", "default browser" NEW due to <https://blog.seamonkey-project.org/2015/11/25/my-unconfirmed-bug-reports/>
I wonder whether observations in comment 2 really are concerning the same problem as original report: d): Test: Menu 'Edit → Preferences → Mail & Newsgroups → Click [Mail] and [News] As expected buttons will become greyed bug: SM did NOT become default email application.
I wonder why nobody else complains because of this problem? We have official 64Bit Linux builds at <http://www.seamonkey-project.org/releases/#linux-x86_64> ...