I'm presonally using QNAP with the Qfile app in in combination with Tailscale, a combination which pretty much allows me to sync and access my files anywhere. However, the issue is that there's no end-to-end encryption of storage unless you specifically mount a Veracrypt volume on your NAS, which is a bit painful to do on mobile OSes. This may or may not be so important because you're not storing your data in some random cloud storage service, but would be nice nonetheless.
However, another more serious issue is that the operating systems and apps of these NAS appliances (Synology and QNAP) are closed source and the companies are both based in Taiwan. I have no way of knowing what the software on these appliances and their accompanying apps are doing and whether they are sending my data back to their mothership. Because of this I'm looking into building a Linux-based rack/tower NAS server using old off-the-shelf parts, but this will take me a while. Using something like Proton Drive in the meanwhile would be nice.
Good. Let's all enjoy Firefox while we can, before WEI becomes mandatory for all top 500 web sites.