Rated 5 out of 5 stars

First, thanks TrVTrV and predecessors for writing this great plugin.

I tried to understand how much work required to convert this plugin to support v68, and realized that the change breaks every UI component this extension is using. The UI component need to completely rewritten, and seems no longer possible to set pull-down menu below the Send button (XUL overlay is deprecated). This mean I have to create an extra Send button dedicated for SMTP Switch.

Also, Thunderbird intends to deprecate XPCOM for extension use in the long term. I don't think it's worth to put the effort developing a new extension when it's known to break some time later, unless they provide a replacement API in MailExtensions that SMTP Switch need to use. (Specifically, querying and setting SMTP server.)