You have a lor of extensions that manage traffic: AdBlock Plus, NoScript, HPTTS Everywhere, uMatrix. It's hard to tell if some of them may be involved. Could you please try reproducing in Safe mode (https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-using-safe-mode) and on a clean profile (https://support.mozilla.org/en-US/kb/profile-manager-create-and-remove-firefox-profiles) so that we can exclude the effect of such add-ons from troubleshooting?
Bug 1587208 Comment 7 Edit History
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You have a lot of extensions that manage traffic: AdBlock Plus, NoScript, HPTTS Everywhere, uMatrix. It's hard to tell if some of them may be involved. Could you please try reproducing in Safe mode (https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-using-safe-mode) and on a clean profile (https://support.mozilla.org/en-US/kb/profile-manager-create-and-remove-firefox-profiles) so that we can exclude the effect of such add-ons from troubleshooting?