Blogpost Version 2017-11-08 (Sprachpaket-Version)
We have a new release: SeaMonkey 2.49.1 (ESR)
Additionally to the official Release Notes here you find some more information concerning changes with SeaMonkey 2.49.
You need a Bugzilla-Account for the queries here in the blogpost. All queries without any liability, because (not only) correct use of TARGET MILESTONE is controversial.
Mistakes in official Release Notes
I don’t know.
I do not know which Firefox52 – features made it into SeaMonkey 2.49.1
A Bugzilla query shows SeaMonkey 2.49.1-specific RFE-Fixes.
More new features
- Bugs in SeaMonkey 2.48 what have been fixed for SeaMonkey 2.49.1.
- Bugs which have been fixed in Firefox and/or Thunderbird since SeaMonkey 2.48. Not all bugs in Firefox or Thunderbird do affect SeaMonkey, but also it is not sure that all fixes will work in SeaMonkey.
Possible new bugs (“Regressions“)
- Possible new bugs in SeaMonkey — only those with Status New or Assigned already have been confirmed as real bugs
- Possible new bugs, caused by regressions in Firefox or in Thunderbird, which also might affect SeaMonkey.
You can find workarounds for new problems in the Wiki
Old and new bugs
A horribly long list, what does not consider that not all Thunderbird– and Firefox-bugs are relevant for SeaMonkey. And many of them are UNCONFIRMED or outdated (have been fixed in between).
SSE2-capable hardware is required for SeaMonkey 2.49 (at least for Windows). A symptom that your PC does not fulfill this requirement might be an error message during installation “… requires WIN XP SP2” although SP3 is installed. 
Pay attention: In (Mail- or HTML)-Composer ‘Rightclick → Languages → Download more dictionaries …‘ will lead to this page “Dictionaries & Language Packs” with a Link to Deutsches Sprachpaket für SeaMonkey x.yz. This language pack is only for SeaMonkey version x.yz and must not be installed for any other SeaMonkey version. Probably the add-on-installer will reject installation – but you never know. And who uses the Add-On-Converter might be seduced to adapt the “Maximum Version” and to install the converted Language Pack (I have not tested yet whether that really would be possible). A Language pack with a version number not matching with SeaMonkey version number can cause serious problems, even make unusable a user profile. Please download Language packs only from seamonkey-project.org.
All builds from download page are for 32 bit systems (as far as I know).
Windows builds will work on 32bit and 64bit systems.
Linux 32bit builds will not run on 64bit systems “from the scratch”. You can try the 64bit build from contrib.
MAC: AFAIK Support for OSX 10.6 to 10.8 has become discontinued already in 2.46 (nevertheless 2.49.1 might be recommended as update version for those OS, and it might to work – you may try on your own risk. Backup your User Profile before you test, I read on mozilla.support.seamonkey (2.46 Automatically Updates, Breaks Mac OS 10.6.8) that this test might damage the User Profile).
And: Nothing we can do about it. Support for those OS version has been removed from the Gecko49 engine and Firefox 49, and so also from SeaMonkey.
See Bug 1257256 – State clearly that Linux builds in Downloads Table are for 32bit only
Chatzilla & DOM inspector
Have been dropped from SeaMonkey 2.49 bundle because of localization infrastructure problems only for this Version. For Details see Bug 1231349 – L10n repacks broken on with SM 2.42 and newer.
If required please download these Add-Ons from AMO:
Catzilla works fine with SM 2.49.1. With an existing User Profile you might not observe that SeaMonkey 2.49.1 has been shipped without Chatzilla, because the existing CZ version still works.
DOM Inspector 22.214.171.124-signed due to AMO is only compatible until SeaMonkey 2.39. Recommended version 126.96.36.199 provided by Adrian Kalla currently can’t be downloaded because of Bug 1287273 – http://l10n.mozilla-community.org/ is down and unresolved Bug 1391525 – Find new Server for Adrian’s Localized Builds. For download link see official Release Notes.
Thanks to all who contributed to the project and helped to make possible this release!