Edge is not free. I wouldn't seriously consider using a non-free application for something as essential as everyday web browsing.
You can't really have usable vertical tabs in Chromium via plugins either, unless you're content with wasting a lot of horizontal space for an ugly sidebar and vertical space for uselessly duplicated tab bar.
Firefox is the only actual choice I'm aware about.
Using Firefox definitely supports the existence of a free browser. Loss of market share is the #1 threat to the continued existence of a free browser. Beyond the obvious (if a tree falls in a forest, crushing the last copy of the code for a browser that has zero users, then was it a browser at all?):
lower market share =>
nobody testing against the free browser or fixing site breakage =>
quirks (bugs, underdefined specifications, nonstandard features) of other browsers becoming required for a functional Web =>
free browser is no longer a browser of the actual Web.
Being controlled by corporate interests is completely orthogonal to being free. A lot of Free Software is being controlled by corporate interests and there's nothing wrong with it.
You can't really have usable vertical tabs in Chromium via plugins either, unless you're content with wasting a lot of horizontal space for an ugly sidebar and vertical space for uselessly duplicated tab bar.
Firefox is the only actual choice I'm aware about.