Please, please, please focus on making the browser better. Hammer home the privacy angle against Chrome. Force Canonical to sit down and fix the Snap launching issues. Open source Pocket and make special features a perk of donating to the browser.
Not sure if this is possible but being lean enough to handle the eventuality of Google refusing to bid to be the default search partner.
I would also like customizability to stop being trimmed away, and ideally for some of the things that users currently accomplish with userchrome hacks to be supported directly one way or another.
The number 1 thing I want to see from Firefox is fist-class support for tree tabs. Using an extension and hacking on userChrome to hide the tab bar is getting tiring, especially with the barriers Mozilla have erected to make user styles more difficult to enable.
That said, I've switched to using the firefox tarball. Start up performance isn't the only issue. Snap firefox doesn't seem to respect my dconf settings and I experienced some strange hangups that forced me to kill the browser.
Not sure if this is possible but being lean enough to handle the eventuality of Google refusing to bid to be the default search partner.