Try going to System Settings > Default Applications > Web Browser:
regardless of my default browser, evolution opens things up in rekonq by default. How might I get this working for firefox?
Choose firefox instead of Rekonq.
If that doesn't work, you might have to configure alternatives for x-www-browser and possibly gnome-www-browser. You can either install 'galternatives' or use the following commands:
sudo update-alternatives --config x-www-browser
sudo update-alternatives --config gnome-www-browser
The answer to the first question might be to install mail-notification-evolution?