Firefox

Nah, I dont use it. In fact, I go through and disable almost all the "extra" stuff in any browser I install. I'm of the "Do one thing well" school of thought, so all these apps trying to do everything, all at once, just to keep you in "their" system? No thanks. Sync offers absolutely zero features that don't have better, alternative options already.

Rarely, mostly due to accessing a cool website I found a few days ago on the device I am currently using

It's a great way to set up Firefox on a new device. Why wouldn't I want to install the same extensions and copy my bookmarks? I wish it also synced toolbar layout so I wouldn't have to remove those weird spacers Firefox adds around the address bar by default every time

I use it, but when I experimented with data synchronization using Firefox Sync, it simply doesn't work, it is so unreliable and unpredictable that you can't bet on it. It's a real pity, because I wanted to use it for a cool thing, synchronizing data of one website, without having my own server for that website. It failed because Firefox Sync fails.

I tried it at two separate times, and both times it would delete my tabs when I add a new device to sync. Maybe I used it wrong, but it just aggravated me to disable it quickly.

I wouldn't have it any other way. I need to have my desktop and phone browsers synced.

I used it accidentally. Now my work PC and my personal laptop have a mishmash of unwanted bookmarks on each

No, because the set up page for it has never actually loaded for me. Ever

Nice try FBI...