Apologies, I completely misunderstood the purpose of this bug. While careful reading of this entire report might have prevented this, I just couldn't reproduce any particular problem with feed messages, regardless of whether "Show article summary instead of loading web page" was enabled or not. Only after some digging on Searchfox did I learn that there is a preference `rss.show.summary` that defaults to "global override, load summary". While this setting itself doesn't show up in the GUI, it prevents all the "Show article summary..." checkboxes under feed subscriptions from having any effect. Not really great UX in my opinion. Anyway, after manually disabling that global override I can reproduce and understand the issue.
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Apologies, I completely misunderstood the purpose of this bug. While careful reading of this entire report might have prevented this, I just couldn't reproduce any particular problem with feed messages, regardless of whether "Show article summary instead of loading web page" was enabled or not. ~~Only after some digging on Searchfox did I learn that there is a preference `rss.show.summary` that defaults to "global override, load summary". While this setting itself doesn't show up in the GUI, it prevents all the "Show article summary..." checkboxes under feed subscriptions from having any effect. Not really great UX in my opinion. Anyway, after manually disabling that global override I can reproduce and understand the issue.~~