Limit JS set cookie lifetime to 7 days

[pes10k]

Safari will start doing this soon, so that gives us some good webcompat cover

https://webkit.org/blog/8613/intelligent-tracking-prevention-2-1/

[diracdeltas]

Should we start with 7 days or shorter (like 1 day)?

[diracdeltas]

2nd question - should this be tied to a shield state or be on all the time?

[pes10k]

For my two cents, i suggest

1. 7 days (so that we can fly under Safari's web compat issues)
2. all the time (otherwise it'd get confusing, do we extend / decrease the life times of existing cookies, etc). Plus, Safari hides the toggle to the point of it basically not existing, so seems like they don't expect web compat issues with it