It depends on how you define quality. With respect to fit and finish, firearms have, generally speaking, reduced in quality. The days of deep, gorgeous bluing, beautiful wood stocks, and hand-fitted parts are long gone unless you intend to pay a premium and/or have custom work done.
However, the quality of machining has improved, generally speaking. This varies based on manufacturer, but I have firearms which have no visible tooling/machining marks on them whatsoever (my Aero Precision AR lowers, my Walther PPQ Navy, my CZ P10C). Additionally, quality with respect to accuracy continues to get better. When I can buy a $200 Thompson Center Compass that can shoot sub-moa (truly sub-moa and not just on a manufacturer's spec sheet), I have to say that quality in terms of accuracy is remarkable and far better than that of even 10 years ago. These examples are more a testament to advances in precision machining technology than anything else, but still worthy of a mention.
Quality in terms of defective products is more manufacturer-specific. I agree with other members that it may seem that there are more sub-par products produced, but that is largely because social media enables those with issues to quickly broadcast their dissatisfaction. However, I would say that I have seen trends of dissatisfaction concerning Remington products over the last few years. With respect to other manufacturers, it's been more model-specific than anything else. The SIG P365 is one example; it got beat up with people claiming to have had issues. I don't dispute that people had legitimate issues. However, I believe that it was a case in which the pistol was hyped up, people experienced issues, lynched SIG on social media, and it gave an appearance as if the the quality of the P365 and SIG, in general, may be questionable. In the same vein, I think it's important to cut manufacturers a little slack. Manufacturers are trying to push boundaries in order to create better products and improve on existing products and ideas. There are going to be lemons, regardless of how much QC and testing is conducted. The good thing is that, in my experience, most gun manufacturers are customer-friendly and will resolve issues encountered by customers.
I am not saying I am right in all my points, but those are simply my observations/thoughts.