User Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:64.0) Gecko/20100101 Firefox/64.0

Steps to reproduce:

Now if there is a problem restoring the session it will say "oops something went wrong" and ask you if you want to restore the tabs and also list the tabs of the previous session and allow you to check which tabs you want to restore or not. Can this prompt be added as an option to make this a thing that always happen? (obviously without the something went wrong message) That way the user can keep the session but decide whether or not they want to restore it the next time or not and which tabs they want to restore.

Something like this

https://user-images.githubusercontent.com/5449042/50862178-8f17ca80-1360-11e9-89a3-34266c575c1a.png

Thanks for the report! So a crash is indeed never user-initiated and if there's a possibility to deal with these situations more gracefully, we should certainly do so.

This effectively means that we can deprecate & remove about:sessionrestore and always restore the previous session after a crash, regardless of the Homepage setting in about:preferences.
We could discuss to keep about:sessionrestore behind a pref to allow users to opt out, but I'm not sure about the value proposition for it; since we have e10s and Fission soon(ish) as well and we only load the active tab in each restored window on startup-restore, I think that the risk of a vicious circle of crash - startup/ restore - crash might've become negligible.
Mike, I'm interested in hearing your opinion re. the risk of doing this.

(Ps. Chrome seems to already behave as proposed.)

If the user is configured to restore their previous session on startup, I think it makes sense to attempt to autorestore the session after a crash[1].

That having been said, I'm not certain that means we can totally get rid of about:sessionrestore. Aren't there other cases it appears that don't include crashes? Cases like:

1. The most recent session file is somehow corrupt - maybe we ran out of disk space, or a bug caused us to write it incorrectly?
2. The most recent session file is missing. The user or some other program got rid of it.

Actually, those are the only two that I can come up with off the top of my head - but if either of those cases are possible, it might be worth keeping about:sessionrestore around as a fallback. Or am I totally off base here?

[1]: I actually probably could be convinced that it makes sense to restore the session after a crash even if the user is not configured to restore the session on startup - but we'd probably want to ask our Privacy folk about that to make sure that's okay.