This is not a new story (Google announced it's plans September 2017), but many people are still unaware that Google Chrome and Firefox will be blocking websites that use SSL certificates issued by Symantec (yes, THAT Symantec) as of April this year. You many think "Well, my SSL certificate was issued by GeoTrust/RapidSSL/Thawte, not Symantec", but the reality is that Symantec provided SSL certificates to many companies (including the ones mentioned) and if you bought one of these SSL certificates, then your website might be blocked.
The result of this is that potentially thousands of websites could be blocked by Chrome and Firefox (there is a more detailed post about this on The Register), but a lot of websites providers still seem unaware that this update is coming. It is of the upmost importance that is your site is protected by an SSL certificate, you contact your provider and ask them if this update effects you!
You might feel that Google has gone to far in doing this, "how can one company dictate the availability of so many websites" you may ask (or at least, words to that effect)? The reality is, Symantec's SSL company has not always been adhering to industry standards when issuing SSL certificates and as such Chrome and Firefox developers feel they cannot trust certificates provided by Symantec. This may be a bit of a frustration for some people, but SSL certificates are supposed to be secure, if there is evidence that a supplier might not be providing secure certificates, it is the responsibility of companies like Google to help protect it's users.
Anyway, if you want to find out more information about the whole story, Google posted an article on their security blog last year, you can go check it out for more info. Google have posted a detailed analysis of why they are doing this and what you can do.
My website is being blocked in Chrome or Firefox and it is after April 2018!
If you are have come to this page after April 2018 and don't know why your site is being blocked, it is your SSL certificate, get it re-issued (or get a new one)!