tl;dr this type of bug will probably be hideously difficult to reproduce. In this situation I’d normally shelve the issue, without a proper report, but the overall behaviour of Firefox – not entirely unresponsive – made me curious, so this morning I spent around three hours troubleshooting. Twenty-eight screenshots, and so on …
… if I attempt a set of written notes, I’ll lose the mental overview. Instead I’ll make a separate post (below) with just two of the twenty-eight shots.
Side note: AMO and restraint
If you want an example of restraint, where a more recent version of an extension is available but automation does not apply, maybe consider Diigo. https://addons.mozilla.org/addon/diigo-web-collector/versions/ – Diigo Toolbar (2013-02-27) was succeeded by Diigo Web Collector - Capture and Annotate (2017-07-19). Neither automated nor manual checks drew attention to this year’s major update …
… I guess, because the start of the Version string is numerically inferior to its predecessor:
Name: Diigo Toolbar
Name: Diigo Web Collector - Capture and Annotate
Notes to self:
diigo_toolbar_annotate_screenshot_bookmark-18.104.22.168-fx.xpi set aside 2017-08-26
3.3.56 abandoned yesterday (back to the 2013 version with its superior set of features).