I don’t care much about “look and feel” but have nearly 10 Firefox add-ons too, which I use because they do things I need doing. I’ll be very disappointed if they don’t work with the new version. Maybe the add-on developers will use the beta versions and prepare for the change, most of them, anyway.
So far I’ve been fairly well satisfied with Firefox, and don’t want to change to a new interface, either within or without Firefox.
I have heard that Chrome is more secure than FF.
Download and try Waterfox. Based on the same open source — “look and feel” pretty much exactly the same, and the Legacy add-ons work with it. (Well, the ones that I use do; I can’t speak for every single add-on.)