I installed Windows XP few days ago, Letsecrypt certificates are working fine on Firefox 43, it just doesn't work if you are using SNI and IE8. Haven't tried Chrome but it must work.
Firefox uses its own certificate store, that's why it works on Windows XP. Chrome and Internet Explorer will likely not work, because they use Windows XP's certificates, which don't include trust for Let's Encrypt.
Their root certificate is currently not trusted by any browser vendor. They have a cross-sign from IdenTrust, which is trusted even by XP. However, their intermediate certificate uses a name constraint in a way that causes schannel (Microsoft's TLS stack) on XP to think they're not allowed to issue certificates for any domain name. Chrome and IE use schannel, while Firefox ships its own TLS stack. This bug was fixed in newer versions of Windows. This might get fixed if someone finds a way to generate an intermediate cert that doesn't trigger this bug (while still including the *.mil constraint).
They are just trying to fabricate another reason. I don't think twitter ban will be lifted before local elections.
And according to twitter policy announcement [1], Turkish government asked Twitter to provide some credential information about some Turkish users. Nobody is talking about this in Turkey and government officials still defending their decision about their fabricated reason: impersonation and porn in twitter. It's already against Twitter's TOS, and I don't think it's true.
In the interests of full disclosure, I have only answered 3 problems on Project Euler, and I did them all myself, because I have the willpower to not look at other answers before creating my own. (I have the same username there: http://projecteuler.net/profile/jcurbo.png) Anyone looking to learn something and not just check boxes will do the work and exert the same willpower to ignore solutions already out there.
The core of this problem exists in education at all levels; the learner must be coerced or convinced that it is in their best interest to actually learn the content rather than cheat.
