[leegraham]

The browser dev tools warn you about it (with links to how to fix it) and I think if you’ve got the change they also tell you which cookies have been blocked. I don’t mean that to sound holier-than-thou, even with the messages I spent a couple of hours last week debugging the exact problem you mention on an internal tool.

[cpeterso]

This is why web developers and testers should test pre-release browser versions. Better to find out that a code change in Chrome Canary or Firefox Nightly broke your website 4-8 weeks before the new browser ships than after it ships. If the breakage is a browser bug, you still have a chance that Google or Mozilla can fix the regression before it affects your users.

[lol768]

There's an argument to send pertinent A/B study information in a request header of some sort, for this reason. It's now no longer enough to just look at the UA.