Hello again, Chacapamac.  Yes, that can be done, if you carefully sign in to Google, switch on Firefox Sync and, although I've never tried this, according to this article, carefully switch on iCloud to sync bookmarks between Safari on your Mac, Safari on Windows and even Internet Explorer.

The carefully are explained in BookMacster's [urlhttp://sheepsystems.com/bookmacster/HelpBook/]new improved Help Book[/url], which we rewrote last week and just uploaded a few minutes ago.  (Your BookMacster app still has the old Help Book until the next update.)  In your case, the instructions for setting up syncing will refer you to the instructions for designing your own advanced sync setup.  In Example 2 on that page, imagine that Dell PC being inside your Mac.

In your case, I think that, since you've already set up syncing your Mac's browsers, all you need do is switch on iCloud Safari syncing in Safari on one Mac and in Safari on Windows.  Note that, when you do that, iCloud will immediately suck any bookmarks from Safari Windows, and maybe Internet Explorer too, into iCloud, and then they'll be pushed down to your Mac, and then BookMacster will push them into Firefox and Chrome.  So if you bookmarks on the Windows side that you already have on your Mac, or don't want, it would be better to delete them first.  I'm not sure how iCloud deals with duplicates.  BookMacster can find and delete duplicates, but it's easier to not create them in the first place.