1. This is just a tracking bug in relation to Win64 Firefox for Release. The Win64 Firefox for Release has existed since Firefox 42.0 and was then listed on
http://www.mozilla.org/firefox/all/ since Fx 43.0 Release.
2. At the moment the current stub installer on Windows since Fx 53.0 is 32-bit but will install 32-bit or if user can use it then 64-bit.
https://www.mozilla.org/firefox/53.0/releasenotes/
3. A rather old bug from July 2006 about a SeaMonkey user having a crash with 32-bit SM on 64-bit Windows Server 2003. Not sure why you linked to this one.
4. For one or more it may have been a hiccup as it is not done intentionally.
5. That was just some tracking on how the
http://www.mozill.org/firefox/all/ page should have in layout of the 64-bit Windows and Linux builds. I get it as In doing support some did not realize that the builds that did not have 64-bit were just 32-bit builds. The Mac OSX only has one row now as it is currently only 64-bit as 32-bit was dropped as of Firefox 53.0 and later.
6. A bug from Sept 2015 about a user trying to build (third-party) a SM 2.40a1 build on Nightly channel at time for 64-bit Linux. Up til SM 2.46 Release (only en-US) the 64-bit Linux builds of SeaMonkey Releases were either from a Contrib folder (were official but not, bit of storey) or by building 64-bit SeaMonkey Releases yourself. Not sure why you linked to this one.
7 and 4: Also the Firefox 51.0 was the first to show if you have 32-bit or 64-bit in About. Some people as a result mistakenly thought they were using Win64 Firefox and were downgraded to 32-bit Firefox when they were actually using 32-bit Firefox all along. I have asked people in threads since where they got Firefox before doing updates including to 51.0 and they said
http://www.mozilla.org. At the time the stub installer (before 53.0 and later) served to Windows users on
http://www.mozilla.org was 32-bit only. They just thought they had Win64 Firefox because they had 64-bit Windows 7, 8.1, or 10. Once they got Win64 Firefox from
http://www.mozilla.org/firefox/all/ they were happy.
8. An old bug from Oct 2009 about somebody building the JavaScript Engine on Mac. Not sure why you linked to this one.
9. A old bug from May 2013 that is not really relevant. Not sure why you linked to this one.
10. It was explained in bug for if you use download button on
http://nightly.mozilla.org/ instead of going to the All Languages and Builds (incl. Win 64) link which is
https://www.mozilla.org/firefox/nightly/all/
AFAIK the stub installer itself is 32-bit but select 32/64-bit Nightly automatically during the installation... See Bug 797208.