My library is synchronized via webDAV, to a server at my university, originally set up by copying the cert_override file from firefox. This worked flawlessly for about six months at least. I sync both my work computer (linux) and my laptop (linux/windows dual boot, library location on a shared partition). Recently I got a sync error on the laptop, checked the "verify server" button in the sync preferences, and got an SSL error. It happened first under Windows on my laptop, but I shortly thereafter switched to Linux and got the same error. I was able to get it working again by recreating the cert_override file and replacing the old one with the new one. I had to do this on all three zotero instances. Each time I did it, something close to every PDF in my library had to be freshly uploaded or downloaded. Then everything worked fine for about a week, and now I'm hitting the same problem again. The only cause I can think of is that Firefox updates are breaking this? I don't recall doing any Zotero updates in the last few weeks, but I do recall a firefox update.