

100% agree.
If its not open source 1) you can’t fully trust/audit. and 2) you’ll be left in the dust should the company cease to exist as nobody can continue development.
If Firefox is not private enough use Librewolf. If you’re interested in something new and exciting give Zen Browser or Floorp (both based on Firefox) a spin.
Can you elaborate? It’s my understanding that push notifications are only used to trigger Signal to check if there are messages - the message data and who/what triggered it is not being sent to Google/Apple. If you don’t trust push notifications, you can always use a De-google’d phone and the Signal APK which will fallback to polling the server; this will obviously impact battery life as the app needs to constantly be checking for new messages.