[Taggregator] Stylesheet access issue

[Lioncat6]

DOMException: CSSStyleSheet.cssRules getter: Can't access rules of still-loading style sheet
    getSourceSheets https://musicbrainz.org/release/48a37e8d-8342-41c9-ac7f-13e160d781b5/cover-art:390
    iterateSourceSheets https://musicbrainz.org/release/48a37e8d-8342-41c9-ac7f-13e160d781b5/cover-art:381
    iterateSourceSheets https://musicbrainz.org/release/48a37e8d-8342-41c9-ac7f-13e160d781b5/cover-art:372
    getSourceSheets https://musicbrainz.org/release/48a37e8d-8342-41c9-ac7f-13e160d781b5/cover-art:388
    handleSheetChangeForNode https://musicbrainz.org/release/48a37e8d-8342-41c9-ac7f-13e160d781b5/cover-art:428
    set https://musicbrainz.org/release/48a37e8d-8342-41c9-ac7f-13e160d781b5/cover-art:541
    addCSSRules moz-extension://8f30a064-db66-428c-bc91-f9be2b706e8e/ MusicBrainz Taggregator.user.js#3:1138
    addImportTagsButton moz-extension://8f30a064-db66-428c-bc91-f9be2b706e8e/ MusicBrainz Taggregator.user.js#3:1409
    VMbpotkm38spt moz-extension://8f30a064-db66-428c-bc91-f9be2b706e8e/ MusicBrainz Taggregator.user.js#3:1505
    VMbpotkm38spt moz-extension://8f30a064-db66-428c-bc91-f9be2b706e8e/ MusicBrainz Taggregator.user.js#3:1507
    VMbpotkm38spt moz-extension://8f30a064-db66-428c-bc91-f9be2b706e8e/ MusicBrainz Taggregator.user.js#3:1508
    ln moz-extension://8f30a064-db66-428c-bc91-f9be2b706e8e/sandbox/injected-web.js:1
    <anonymous> moz-extension://8f30a064-db66-428c-bc91-f9be2b706e8e/ MusicBrainz Taggregator.user.js#3:1
MusicBrainz Taggregator.user.js:1508:28

https://musicbrainz.org/release/48a37e8d-8342-41c9-ac7f-13e160d781b5/cover-art

Not sure if another script is causing this