No matter which restore function I use, only the very first tab is being restored and the rest are being ignored. It looks like a great addon but it simply doesn't do it's job. For now, this addon serves me as a backup list of my tabs for when Firefox's sessions restore fails. Firefox Stable v66.

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Cant seem to reply to the response so I'm editing my review:
No difference. After some investigation, it seems that there must be a Firefox preference (perhaps via my user.js file) that is set causing the "bug" (disabling all addons did not help). Debugging this would require moving user.js elsewhere out of the profile directory, then opening Firefox and going through about:config, manually resetting all modified preferences: not ideal. Any idea which preferences you addon relies upon to be functional (and note them on the addon's page)?

When using this addon with a new profile, it works as intended.