I've been using floccus (https://floccus.org https://floccus.org) for quite some time. It's a browser extension available for Chrome and FF that syncs bookmarks

I've been using floccus (https://floccus.org https://floccus.org) for quite some time. It's a browser extension available for Chrome and FF that syncs bookmarks to a WebDAV server. I had the occasional sync conflict where I needed to re-initialise the sync, but it mostly just worked fine. I've recently switched to using Safari more and to sync that, you'll sadly need a macOS running e.g. Synkmark (http://www.sheepsystems.com/products/ http://www.sheepsystems.com/products/). Edit: I think the iCloud tools for Windows also can sync bookmarks between Safari and e.g. Firefox or Chrome.