Hi alexsoko, Firefox doesn't have separate settings for startup page and home pages, as you discovered. Two common workarounds are:

(A) Pinned tabs

If you "pin" the two email tabs, they will be restored at startup (assuming you don't delete history at shutdown). More info on this feature: Pinned Tabs - keep favorite websites open and just a click away.

(B) Customized shortcut

This is based on Windows and I don't know how "shortcuts" work on Linux

Your Firefox shortcut command line can be modified with URLs to open when you launch it.

For example, if you right-click the shortcut and click Properties, then the Shortcut tab, the "Target" field usually looks similar to this:

"C:\Program Files\Mozilla Firefox\firefox.exe"

You can add on URLs like this:

"C:\Program Files\Mozilla Firefox\firefox.exe" -url "https://mail.google.com/mail/#inbox" -url "https://outlook.live.com/mail/"

Hopefully one of those will be useful.

Both of these were pretty close to the desired behavior so I consider this solved! I ended up creating a desktop launcher for what I wanted and pinning it to the bottom panel using the linux version of the second thing you suggested (in linux the command that gets passed to the terminal is just: firefox https://mail.google.com/mail/u/0/#inbox https://mail.google.com/mail/u/1/#inbox). The pinned tabs worked well too, but could annoyingly be unpinned just by clicking and dragging which is too easy for me to accidentally do if I'm dragging something to a new window that is near the pinned tabs in its original window.

Both were pretty close so I consider this solved! The second solution was actually a bit closer to what I wanted as pinned tabs can be unpinned possibly accidentally just by dragging. I just created a launcher for firefox that passed the command: "firefox https://mail.google.com/mail/u/0/#inbox https://mail.google.com/mail/u/1/#inbox" which launches firefox with those two tabs open and pinned them to my bottom launcher. Thanks for your help in leading me in the right direction!