gnome-shell-extension-mpris-indicator-button VS adw-gtk3

Mpris Indicator Button is pretty cool too, but seems to lack a hot key to display it.

I also use the mpris indicator extension myself and that particular dev uses Fedora (or sometimes Ubuntu), and they've said in the past they can't update the extension until Gnome 43 hits, so since Fedora is still delayed to mid-November, that extension won't be officially updated just yet. But if you check their GitHub they have a "crude" master update for Gnome 43 you can use if you really want to, but just know it's not release ready yet.

Extensions: Blur my Shell, Tray icons Reloaded, Clipboard indicator, GSconnect, MPRIS Indicator Button, Night Theme Switcher, Color Picker

There are at least two extensions which do that (for Gnome 40): MPRIS Indicator Button and Media Controls.

Since Waterfox is based on Firefox and the MPRIS implementation of the latter seems optimal I suppose something is "missing"(?) in Waterfox sourcecode, I use the "MPRIS Indicator Button" GNOME shell extension and it's always worked flawlessly with Firefox but it never did with Waterfox .

Use this theme

As far as I know it doesn't exist yet... but most likely Evince will be ported in the future. But while that doesn't happen, what you can do is use the adw-gtk3 theme (https://github.com/lassekongo83/adw-gtk3) for legacy applications to combine with applications that are already ported to libadwaita

Why not use the adw-gtk theme for gnome to make all the deco's match rather than use Adwaita-Dark?

Application Theme : adw-gtk-3 with Gradience

You can use the adw gtk3 theme. https://github.com/lassekongo83/adw-gtk3

GTK theme: adw-gtk3

That's because i use this KvLibadwaita and adw-gtk3 themes to have everything looking the same on Gnome :>

Just found a workaround for the issue until an update fixes the issue for Fedora 28 - Alt+F2, type "r" to restart Gnome Shell. More info: https://github.com/lassekongo83/adw-gtk3/issues/213

I believe that adw-gtk3 could still be beneficial in ensuring a uniform appearance across both GTK3 and GTK4 applications. The more solutions we can offer to users, the greater the likelihood of achieving the desired outcome.