I think maybe (?) this might specifically reproduce **when the URL in question redirects to some other site**. This leads me to suspect that maaaaybe this is a rergression from (or related to) bug 1668083. I can reliably reproduce this if the URL that I enter into my URL bar is `view-source:https://support.mozilla.org/` (...and importantly: after I hit `Enter`, this redirects to `view-source:https://support.mozilla.org/en-US/`) If I instead type in the full URL (including the `/en-US/` suffix), `view-source:https://support.mozilla.org/en-US/`, and then I hit enter, then I get EXPECTED RESULTS -- undo-close-tab works properly. As further confirmation of this theory: I can reproduce this bug using these URLs (which both redirect to their `www.` subdomain): `view-source:https://yahoo.com` `view-source:https://google.com` ...but if I include `www` (avoiding the need for a redirect), then I cannot reproduce anymore.
Bug 1757458 Comment 2 Edit History
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I think maybe (?) this might specifically reproduce **when the URL in question redirects to some other site**. This leads me to suspect that maaaaybe this is a regression from (or related to) bug 1668083. I can reliably reproduce this if the URL that I enter into my URL bar is `view-source:https://support.mozilla.org/` (...and importantly: after I hit `Enter`, this redirects to `view-source:https://support.mozilla.org/en-US/`) If I instead type in the full URL (including the `/en-US/` suffix), `view-source:https://support.mozilla.org/en-US/`, and then I hit enter, then I get EXPECTED RESULTS -- undo-close-tab works properly. As further confirmation of this theory: I can reproduce this bug using these URLs (which both redirect to their `www.` subdomain): `view-source:https://yahoo.com` `view-source:https://google.com` ...but if I include `www` (avoiding the need for a redirect), then I cannot reproduce anymore.