Bugzilla

Going slowly through the steps to reproduce:

From fresh profile.
Login to stack overflow only.
Note that the cookieDB's raw entry for the login cookie is a PARTITIONED cookie with a stackexchange Domain attribute (samesite=None):
```
38	^partitionKey=%28https%2Cstackoverflow.com%29	acct	<value>	.stackexchange.com	/	1756156315	1740517915669428	1740517915669428	1	1	0	0	0	2	0
```

After logging into the stackexchange portal then we note a similar, but UNPARTITIONED cookie:
```
57 <empty partition>	acct	<value>	.stackexchange.com	/	1756156714	1740518314754910	1740518314754910	1	1	0	0	0	2	0
```

So again from fresh profile, I login only to stackoverflow and then manually remove the partitionKey entry from the cookie DB and restart firefox, then the button from stackoverflow "go to full inbox" works!

Still need to look into the desired behaviour:
1. Should the partitionkey have been set at all?
2. Should the browser be sending it anyway?

Going slowly through the steps to reproduce:

From fresh profile.
Login to stack overflow only.
Note that the cookieDB's raw entry for the login cookie is a PARTITIONED cookie with a stackexchange Domain attribute (samesite=None):
```
38	^partitionKey=%28https%2Cstackoverflow.com%29	acct	<value>	.stackexchange.com	/	1756156315	1740517915669428	1740517915669428	1	1	0	0	0	2	0
```

After logging into the stackexchange portal then we note a similar, but UNPARTITIONED cookie:
```
57 <empty partition>	acct	<value>	.stackexchange.com	/	1756156714	1740518314754910	1740518314754910	1	1	0	0	0	2	0
```

So again from fresh profile, I login only to `stackoverflow` and then manually remove the partitionKey entry from the `acct` cookie for `.stackexchange` host in the cookie DB and restart firefox, 
then the button from stackoverflow "go to full inbox" works!

Still need to look into the desired behaviour:
1. Should the partitionkey have been set at all?
2. Should the browser be sending it anyway?