Ah! Ok. Got it.

This is caused by a recent regression bug in Firefox. See https://bugzilla.mozilla.org/show_bug.cgi?id=1535068

We'll see if there's a way to get around this somehow but the problem is that it works fine on Windows but not on Linux or MacOS.

Workaround: open about:config and set "ui.context_menus.after_mouseup" to true.

Please see Feedbro help for a list of keyboard shortcuts. You can open the Help by clicking the ?-icon in the Feedbro toolbar. You can use j/k or shift-rightarrow/leftarrow to move between next/previous item on the list.
Page down/up and space bar affect the actual article view in viewmode 3 as intended.

You can change view mode with the toolbar buttons. Titles-only view can be also activated with keyboard shortcut '2'. See Feedbro help for more tips.

Feedbro does support Reddit feeds but they don't work if you have "Trackers" set to "Always" in Firefox options. This setting blocks all XMLHttpRequests to Reddit. You need to set it to "Only in private windows" because Firefox still doesn't support whitelisting of sites.

EDIT: Feedbro 3.41.7 now supports X-Frame-Options modification so view mode 6 should work for all sites.

Note that you have to set "Trackers" setting to "Only in Private Windows" in about:preferences#privacy if you want to load Reddit feeds. This is because Firefox has an internal "tracker list" where Reddit is blacklisted. So Firefox blocks all XMLHttpRequests to Reddit if you have Trackers setting set to Always.

Other than that I guess your comment is valid especially for view mode 6 (embedded iframe view). Some sites send HTTP Response headers that prevent embedding their site in an iframe. We'll check if it's possible to get around this without introducing performance penalties or other side effects.

1. Yes it's intentional that items marked as read aren't hidden right away. This gives the user the possibility to "undo" the mark as read operation.

2. That's true. Note that you can collapse by pressing Enter but currently "closing by clicking" isn't supported. This is because closing isn't really needed and a careless attempt to click a hyperlink in the article could result in collapsing the article which could infuriate some users (we tested this :)).

3. Custom CSS support would be easy to implement but the CSS hasn't been very stable (we have changed it a lot along the way) which could easily lead to breaking custom CSS configs and an avalanche of support requests and complaints. So it hasn't been implemented so far. We are open to all UI improvement ideas though.

Feedbro has built-in partial feed->full text feed engine. Right click the feed in the feed tree, select Properties and then experiment with the "Feed Entry Content" setting (change it + click Preview). Then Save. New articles loaded after that will use the new setting.

It doesn't work like that. Timezones are taken into account in date stamps. So any article will become immediately visible regardless of timezone differences as long as the timestamp of the article is not in the future. For example if some feed contains an article timestamped to year 2124, it won't become visible before that year is actually active. It sounds like in this case the feed posts some articles so that they are datestamped to the future.

If you want more clarity with this, please send the feed URL and your timezone info to feedbro.reader@gmail.com

EDIT: the reason Feedbro doesn't load articles that are timestamped to the future is that it would complicate many things. For example if you have a Rule that would popup a notification when a new article arrives, should that Rule trigger when an article is loaded that is timestamped in to the future? Probably not but then when should it trigger? That would then require some background scanning process to find articles that haven't been triggered by rules but are already in the database... etc. It would complicate and slow down the code quite a bit. Unless the feed is super floody, Feedbro will eventually load the article so it shouldn't really be an issue. And this is relevant for maybe 0.001% of the feeds out there so it's an obvious WON'T FIX decision.

The feed probably has markup that has hardcoded font size?

Feedbro does not cause the corruption. IndexedDB corruption can occur when Firefox updates. The profile/IndexedDB functionality completely breaks (has nothing to do with Feedbro) since it breaks for all add-ons and websites. There are bugs about this in Bugzilla.