I switched to bitwarden when I started using firefox 57 beta and lastpass didn't yet have a webextension version. Now that lastpass does have a webextension version, I haven't bothered switching back.
If your computer were a city, the web browser would be the high crime area. I may have my valuables in a locked safe, but it's a little bit self-defeating to carry that safe with me in the places where I'm most likely to be mugged.
On the other hand a website should not be able to get at any password stored in (or pasted into) the browser except its own.
Edit: Spent 30 seconds to troubleshoot. If I disable uBlock Origin and then login to LastPass (extension), it works fine. So just a small conflict somewhere. YMMV.