Hi, you say Proxy add-on. You do not say what proxy add-on nor have you mentioned that you have gone to the Developers page of that Proxy add-on to look for Support, as there is. As well possible FAQ's and contact information. Mozilla only ok's Extensions submitted by Developers to be used with Firefox. They ok them only and give the Developer a web page to distribute their Extension from. You are also running a beta program. This may be fixed next update, or not. The add-on may not be compatible with version 60 of Firefox, contact the Developer for more information. Once you have contact the Developer for support and there is no work around or options maybe If you have a bug, file a bug report. https://bugzilla.mozilla.org/ Bug Writing Guidelines : https://developer.mozilla.org/en-US/docs/Mozilla/QA/Bug_writing_guidelines Please let us know if this solved your issue or if need further assistance.