Thank you for you review and your requests :-)

Drop feeds has already 2 vertical column layout one for feeds, another vertical column for article-titles (option Items / Feed items list).
I will think to add a 3rd column for article content (but I am not sure it is good idea because articles will display in small area, and will be difficult to read, but if it is what users want, then I will do it)

Yeah you are right, Drop feeds needs a dark theme.

But these improvements will not come on the next version 0.9 (close to be ready and coming soon) but may be in 0.9.1 or 0.9.2 you will see ;-)

Edit:
Like as I said I will do it (3rd vertical column layout), and yes I will take a look to other RSS addons.

Edit2:
Thank you :-)

Edit3:
- I have take a look to FeedBro but I haven't the 3rd layout in the left column, but may be I haven't look well.
- I have tried too to take a look to NewsFox, but is not compatible with actual Firefox version, and I have tried to install it on Firefox 56, but unfortunately it has failed (I haven't investigate why...), then I haven't no example to base on, and see what you expect exactly...
- Any way I have made a 3rd layout, it is available on github: https://github.com/dauphine-dev/drop-feeds/releases/tag/0.9.1alpha4 . If you have any remarks please tell me in the discussion thread devoted to this development here : https://github.com/dauphine-dev/drop-feeds/issues/64

Have fun with Drop Feeds 0.9.1alpha4 ;-) (it is a incomplete work, but it is a working version)

Edit4:
The 3rd layout and dark themes are now available in Drop Feeds version 0.9.1