This is Facebook's decision. Mozilla Firefox just displays the content that Facebook sends to your device.

You can contact Facebook about this at https://www.facebook.com/help/contact/268228883256323

Thank you for your time and response. okay..we were just wondering about the latest update of firefox beta for android version 52.0. Why did the version Before that we had installed on several different smartphones of ours and we all Were able to view, access and interact with All of our facebook messages without having to either be force directed to install facebook messanger or even selecting the "Request Desktop Site" Methonds? Why, what, who in the updated latest version of Firefox beta for android do users now have to do either of above mentioned methods to check our facebook messages, But not before the new update and Not in the regular firefox browser for android??

Facebook makes changes to their website on a weekly basis. Most of them are minor or not user noticeable changes. However they have been slowly expanding their blocking mobile browsers from accessing messaging (article dated June 6 2016). The release of 52 beta is just coincidence.

You can also try the website https://mbasic.facebook.com which is a version of the Facebook website that is designed for slow connections.