I want to have a separate Firefox profile for my Google-Account, primary used by Gmail.
I use Linux Mint 19.3 Tricia.
I want to have an own icon in the task list, and the Gmail profile should not be opened in the Firefox "Icon Group" (don't know the correct name)

Steps to Achieve That

1. Create a new Profile
   1. run Alt+F2
   2. enter firefox -P
   3. Add new profile, call it "Google"
2. create a new file ~/.local/share/applications/GmailFF.desktop and with this content:

   [Desktop Entry]
   Name=Gmail Firefox
   Exec=firefox -P Google --no-remote --class GoogleFF
   Comment=Open Firefox with Google Profile
   Terminal=false
   Icon=checkgmail
   Type=Application
   StartupNotify=True
   StartupWMClass=GoogleFF

   The magic is coming from StartupWMClass, now Firefox for profile Google opens like a different program (found at https://www.techrepublic.com/article/how-to-run-two-different-firefox-profiles-at-once-on-linux/)

3. Search for "Gmail Firefox" (or whatever Name you defined above) and open the profile.
   1. Pin the program to the tasklist
   2. Log in to Gmail-Account
   3. Change "Homepage and new windows" to gmail.com in Preferences
   4. Change "Default Search Engine" to Duckduckgo in Preferences
   5. Install add-ons Ublock Origin and Privacy Badger