...More often than not once you run a few FF in various places sync just scrambles everything into a pile
When I read that, I thought I should mention that my experience of using FF (Beta update channel) is that, quite to the contrary to what you stated, FF Sync works like a charm.
The only real problem I have had with FF tends to be what is an apparently common recurring problem that, on the beta update channel, with all the frequent updates, FF performance tends to occasionally decline/misbehave to the extent that the only way to fix it is to start FF up in base form (i.e., without any add-ons, etc.), and then re-install all the add-ons and Greasemonkey scripts etc. manually. I got the advice to do that from some helpful forum/blog posts, and it turned out to be good advice.
However, there was a real problem with following that advice - you are then forced into a seriously tedious exercise of manually re-installing all the add-ons and other stuff, which is a proverbial PITA.
I discovered that I was able to automate it all (except for Greasemonkey scripts) through the use of FF Sync, which automatically re-installs all the add-ons and other stuff (e.g., including bookmarks) that you can choose to sync. You may have to manually reset some settings, but that's about it.
However, I had to reinstall the Greasemonkey scripts manually, which was another PITA. Then at some stage a Greasemonkey update introduced an option to "Enable Firefox Sync for User Scripts", so that got rid of the PITA.
FF Sync has been operating thus, apparently faultlessly, for me and for a long time. I changed to the latest version of FF Sync some time back when they first introduced it. Sync has enabled me to sync FF smoothly across 3 computers, even with up to 3 different users sharing/syncing things like the FF bookmarks on those computers. FF Sync is pretty smart.
The only surprising thing I find about FF Sync is that it doesn't
scramble the stuff up.