Connector incompatible with first-party isolation?

I have had intermittent problems with saving to Zotero from Firefox on Linux x64 (Manjaro). Sometimes re-opening one or other application fixes the issue. However today I just couldn't get anything to work - even standard cases like youtube videos or Google Scholar citations. I am currently on Zot 5.0.38 and Zot Connector 5.0.35 in Firefox 59.0.1 (64-bit). Looking at the extension prefs I saw the following repeated in the error log:

[JavaScript Error: "First-Party Isolation is enabled, but the required 'firstPartyDomain' attribute was not set." {file: "chrome://extensions/content/ext-cookies.js"}]

[JavaScript Error: "First-Party Isolation is enabled, but the required 'firstPartyDomain' attribute was not set." {file: "moz-extension://0020f76f-38e9-41f2-872c-1677b863cb28/messaging_inject.js" line: 76}]

Debug ID: 1938659786

I realised the issue may be caused by my manually-enabling first-party isolation in Firefox following the Meltdown/Spectre vulnerability reports in January 2018. Lo and behold, disabling first-party isolation immediately fixed the connector issue. Strangely, I have had isolation enabled for ~2 months, with connector working during most of that time (added ~30 items from browser during those 2 months).

TL;DR Is first party isolation in browser supposed to be incompatible with Connector, or is this a bug?

Thanks,
Adam Russell
This discussion has been closed.