That annoying scroll-to-top happens to me too and I use the latest Firefox version on Ubuntu. I first noticed it several months ago.

Also, some time ago, when you clicked a message to view it's context, Twitter would expand the message list inline. Now it takes you to a new page and when you return you're back to top.

Firefox. I could also trivially avoid it if they used real links, such that I could middle click to open in a new tab, but since everything is just a div with an onclick handler, that's nigh impossible.