How portable is Firefox Sync to other browsers? I find myself in need to keep both Firefox and Chrome open at all times (different websites work better with either of them). I would like to have at least my bookmarks and passwords synced—don't really care for history or tabs.

LastPass and others provide a cross-browser password sync service. But after Xmarks having been discontinued, I could not find find any cross-browser bookmark sync service. I was hoping Firefox Sync would be open enough for someone (preferably Mozilla Foundation) to have built a Chrome extension to support it, but this hasn't happened, and doesn't even seem to be on the works.

I'm actually willing to pay a subscription for this functionality (i.e. bookmarks/password sync across the the major browsers) for anyone who supplies it without trying to lock me in their service or browser.