Thanks for taking the time to share your experience with us, and we're really sorry about your experience. Would you be able to share some details with us via support.zenmate.com so we can identify the problem since ZenMate doesn't interfere with any other add-ons?

::UPDATE::

Upgrading your Firefox browser to Firefox Quantum automatically removes old add-ons that are incompatible with the new version of Firefox. This is not an issue that is caused by ZenMate, but by upgrading your browser. For more details on add-on compatibility with Firefox Quantum, please refer to https://blog.mozilla.org/addons/2017/09/28/webextensions-in-firefox-57/

Thanks!