I'm not sure whether first-party isolation is already enabled by default, so did you enable it yourself ?

• https://searchfox.org/mozilla-release/source/modules/libpref/init/StaticPrefList.yaml

See:

• https://developer.mozilla.org/en-US/docs/Mozilla/Firefox/Privacy/State_Partitioning
• https://hacks.mozilla.org/2021/02/introducing-state-partitioning/

I'm not sure whether first-party isolation is already enabled by default, so did you enable it yourself ?

• https://searchfox.org/mozilla-release/source/modules/libpref/init/StaticPrefList.yaml

See:

• https://developer.mozilla.org/en-US/docs/Mozilla/Firefox/Privacy/State_Partitioning
• https://hacks.mozilla.org/2021/02/introducing-state-partitioning/

I turned it on, but I want to turn it off for this one site and keep it on for others such as youtube

Here's what FPI does:

Let's say Ad Network sets a third party cookie on 12 sites you visit.

Normal: Firefox stores and returns that as a single cookie, which allows Ad Network to track your browsing on 12 sites in a single profile.

FPI: Firefox stores those cookies per site so it stores and return 12 different cookie, depending on which site you are visiting. Ad Network ends up with 12 different profiles, one for each site, and -- absent some other data to connect them -- cannot connect the dots.

Of course, Firefox's anti-tracking feature, and add-on ad blockers, will take care of a lot of that problem, so if you don't use FPI, you probably end up somewhere in between.

All that said, I'm not aware of a way to set exceptions. What is the add-on author's explanation for why it is needed?

Here's what FPI does: Let's say Ad Network sets a third party cookie on 12 sites you visit. Normal: Firefox stores and returns that as a single cookie, which allows Ad Network to track your browsing on 12 sites in a single profile. FPI: Firefox stores those cookies per site so it stores and return 12 different cookie, depending on which site you are visiting. Ad Network ends up with 12 different profiles, one for each site, and -- absent some other data to connect them -- cannot connect the dots. Of course, Firefox's anti-tracking feature, and add-on ad blockers, will take care of a lot of that problem, so if you don't use FPI, you probably end up somewhere in between. All that said, I'm not aware of a way to set exceptions. What is the add-on author's explanation for why it is needed?

The author didn't say anything on it, rather, I found that the exstention would report the that you weren't logged in when I had FBPI on. The author is well trusted within the cummounity and the exstention is open source

github: https://github.com/ScratchAddons/ScratchAddons

See also:

• 1556212 - Per-Domain Cookie Permissions are broken with FPI enabled

First Party Isolation is not a supported feature of Firefox; it's included to make it easier for the Tor Project to maintain their browser. You want to disable FPI in about:config and set Enhanced Trackign Protection to 'Strict' in Settings-> Privacy and Security. This will enable Dynamic FPI which is very similar to FPI, and is a supported feature.