While Vivaldi is currently available gratis (without monetary charge), it is currently not fully libre (meaning that it does not allow users to view the source code used to create, to modify that code, or to redistribute modifications) and is, therefore, neither free nor open-source software. The...
Opera is full of user controlled settings. Everything can be imported and exported even RSS feeds. It can be skinned in a variety of different themes or it can be extended through the use of a large number of plugins available.
With the new release (as of Dec 6th 2016), you can save a group of "Sessions" with logins stored to a Project, which you can launch with the click of a button. "Projects" eliminates the need to spend time setting up your workflow every day, so you can get right to work.
Believe it or not, Safari has amazing dev tools, To enable them, go to the Preferences -> Advanced -> Show develop in the menu bar. There are many many options to help you with mobile site development, and much more.