Disclaimer: I'm writing this on Firefox. I was one of a couple of ten thousand people who donated money ten or so years ago for their famous NY Times ad when they were still going head-on against IE. I like them.
This being said: if their Sync platform works for you, great. Here are my reasons why I choose 1Password as my password manager:
1. It's made by a company that focuses exclusively on this one product. It's their raison d'être, not a side project.
2. They're old-fashioned in a way: they provide me with something, and I give them money for it. 1Password is not cheap, but very good value for money - for me.
3. I've been using it for over half a decade now. 1. and 2. together give me a good reason to believe I can continue to do so for a long time to come. This is in stark contrast to Mozilla, who have been throwing stuff against the wall for quite a while now and abandoning it whenever things do not pan out
4. Various sync options. I'm not required to trust any one "cloud" provider when it comes to privacy, security or continued availability
5. The 1Password vault format can actually be opened in a browser. Even if by some strange fluke I find myself without a client, I can simply download the file on pretty much every machine and still access my passwords
6. UI. 1Password is very well thought out, and that's an important thing for me for something I use about a couple dozen times every day.
While I cannot swear to it, I think I only paid twice over the last six years - the initial purchase plus one paid upgrade some time in the middle. I actually hope to pay for the next one; not only because of what I consider to be fair, but because I want them to do well and be around a long, long time.
And when it comes to security, I've seen HN's resident crypto luminary tptacek give it his thumbs-up. This is something I am not able to properly assess on my own, so his word is good enough for me.