Site data cleared too aggressively in container tabs

[richardb64]

Before submitting a bug report

• I updated to the latest version of Multi-Account Container and tested if I can reproduce the issue
• I searched for existing reports to see if it hasn't already been reported

Step to reproduce

To reproduce, just use containers for their intended purpose, ie. as a way to isolate browsing between sites, or to enable multiple independent sessions on a single site.

All privacy-related general settings are set to default values (eg. delete-on-exit is not enabled).

Actual behavior

Browsing in containers seems to forget cookies and other site data faster than it should - it's hard to be specific, but certainly a lot quicker than the server-specified expiry would suggest. Data survives a simple browser restart, but in many ways containers seem to behave more like private tabs than normal tabs.

Additionally, and possibly related to the same underlying issue, "open frame in new tab" is losing site data, again in a way that doesn't happen for normal non-container tabs. It is as if the security profile (CORS, etc) is different between container and non-container tabs.

Expected behavior

Container tabs should behave in all respects identically to normal tabs, with the sole exception of site data being segregated. The lifetime of site data, and any security-related policies, should be identical to normal browsing.

Additional informations

I suspect that the problem here is actually in the Firefox core, since the Multi-Account Containers extension is essentially providing a GUI to otherwise hidden core functionality. If a Firefox bug therefore needs to be raised, then I can of course do that, though perhaps the extension devs will be in a better position to suggest specific areas of investigation.

Provide a copy of Troubleshooting Information page (optional)

No response