I don't know if any marketing could have helped Firefox not lose to the shitty dark practices from the three other browsers you mentioned:

- Chrome: Spam ads for Chrome on all Google services (incl. YouTube and Google Search which probably are the two most visited websites on this planet?) - Safari: Make it the default and prevent users from using any other browsers (on iOS every browser is Safari under the hood and will reports as such to browser census) - Edge: Make it suck less and also make it really hard to remove it from your system or switch to a different browser

Defaults matter and, especially when they are this toxic, they are hard to beat :/