Not really, I get https://download.mozilla.org/?product=thunderbird-52.0.1-SSL&os=win&lang=en-US. Which locale are you in. Andrei, can you please take a look here.
It's offering this version because the user agent is for Windows XP (Windows NT 5.1). TB52 supports XP right?
We need to offer 38.5.0 to XP users because it's the last version that supports SP2. There's no way to distinguish SP2 vs SP3 by useragent(as far as I know) for the website, and so updating past 38.5.0 is left to the client's updater if need be. In short this is working correctly, if we offer a more up-to-date version it would provide an installer that simply won't work on some versions of XP.
Thanks for the explanation. Now I have another problem about distribution: My TB52.0b4 receives update notification of 53, but 53 is not for my XPsp3 (I once updated and cannot start TB). This is another problem but I am just lazy to open another bug. :)
Thanks, I filed https://bugzilla.mozilla.org/show_bug.cgi?id=1357971 Versions of TB past 52 won't support XP any longer and the beta channel shouldn't be updating XP users.