Rated 4 out of 5 stars

Sporadically, directly after installation of this add-on or after (re-)starting TB, instead of the small XNote pop-up window when opening a mail with a note, an error message is displayed:

XML Parsing Error: no root element found
Location: chrome://xnote/content/xnote-window.xhtml
Line Number 1, Column 1:

In this state, the XNote can be seen below the mail header, but without the XNote pop-up, the note cannot be modified. Possibly the same error as reported for Mac – I'm on Linux (Ubuntu).

Disabling and enabling the add-on seems to fix the issue temporarily, but that's not pretty.

Any pointers? opto, can I provide any info for debugging? Let me know.

In the moments it works, it's a pretty nice add-on, though! Only the XNote column in the message list doesn't seem to work. And I vaguely remember the old XNote (TB3+) had an XNote icon in the message list, which would be nice here as an option, as well.

TB 91.8.1 on Ubuntu Linux 20.04
XNote 3.2.10

Update 2022-04-29:
Another thing I have observed: Ever since first installing this add-on yesterday, I noticed TB slowing to a crawl most of the times when a mail with an XNote is involved in the current view, e.g. when switching to the mail folders' tab or to the tab with the opened mail. In those moments, TB fails to react for several seconds until finally the selected tab is displayed. However, this delay in responsiveness remained even after uninstalling this add-on. So by now I am really puzzled whether it even has to do with the add-on. Might as well be a totally unrelated issue with TB itself which I just happened to notice the first time yesterday.

This review is for a previous version of the add-on (3.2.10).