I've used Firefox at various times in the past, but until recently was using Chrome. Since Quantum came out, I have made that my primary browser on all my machines - Windows 10, Mac, and an Android phone. On the Mac I imported my extensive collection of bookmarks (>55,000) from Chrome and turned on Firefox Sync. That worked at first, in that those bookmarks appeared on the PC. But some hours later they were replaced, on both Mac and PC (not sure about the phone), by a very old set of bookmarks the Sync system must have saved from one of the times I was using earlier versions of Firefox - they are mine, but definitely not from any of my current machines. Fortunately, I had backed up my current bookmarks, so I deleted all of the ancient ones and imported the current ones from that backup (which took forever, but let's not worry about that now). Once again, that worked for a while, but then the ancient set replaced them on both platforms. Again I deleted them and restored from my backup of the current ones, but yet again they've been replaced by the ancient ones.

Needless to say, this is annoying. How do I get it to stop? And more generally, is there some way I can set one of my machines as the master for sync purposes, so its bookmarks always get propagated to my other devices and they never get replaced by Sync?