Someone has forked Tree Style Tabs so that it works with latest Pale Moon.
Tab Center Redux <https://addons.mozilla.org/en-US/firefox/addon/tab-center-re... is a fork of the testpilot extension that is a WebExtension, so it works fine in Firefox Nightly. It's naturally more limited than the original extension, though: it can't hide the top tab-bar, it has to draw its own context-menu, it can't be shown at the same time as any other sidebar, etc.
It's still nicer than the top tab-bar for those of us with a bunch of tabs open, though.
Set your User-Agent to Firefox or IE Edge and Windows OS. You'll soon see "install chrome" pop ups/banners/warnings that take up a portion of the screen all over Google properties.
At that point why not just self-uninstall?
Out of non-Google search engines, Yahoo makes most sense even if they got no money from the deal. Maybe DuckDuckGo but unfortunately it's still not as good.
Regarding extensions, it's better this way because nobody is bothering with current API. Most new extensions are chrome-only.
This is a US only move, in the EU it's still google and mozilla got a truckload of criticism for this.
Firefox is about to shoot itself in the foot again. Soon, all old add-ons will stop working, as Firefox tries to get add-on developers to change to their new WebExtensions API. (Which is almost, but not quite, compatible with Google's add-on format.) Many developers are not bothering, and will drop Firefox.