* Don't break default account config when folder mapping of a non-default account is changed.
* Detect attachments automatically on issue creation and updating (on Thunderbird 91 and later).

* Open clicked URL with the default browser if possible.
* Handle custom fields added to fetched issues correctly.
* Support default configs provided via managed storage.

* Open link in the default browser on Thunderbird 78.6 and later.
* Fix hanging with blank dialog on slow Thunderbird situations.

Fix regression: fallback to "link to issue" correctly when the updating message is not yet linked to any issue.

* Fill parent issue id correctly on updating issue.

* Initialize custom fields correctly with blank value.
* Fetch and apply currently saved value of custom fields on updating of issues.
* Add ability to set default account and inheritance.
* Allow to link partial threads to different issues.
* Add ability to link selected messages to an issue.

* Support Thunderbird 78.
* Support multiple accounts.
* Support contextual menu command.
* Add menu button to the message header area.
* Add ability to log time entries when updating issues.
* Add ability to remove last quotation part from the message body.
* Add ability to paste images from the clipboard.

Know restriction:

* Cannot extract attachments automatically. You need to save attachments to your local disk and drag & drop files to the dialog manually.