New: LibreWolf (Dec 03, 2022), Platform 23.0 (Dec 9, 2022)
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What about Abilon? http://www.abilon.org/
It saves news and memories somewhere on the local computer but it doesn't need any setup. I would call it half portable.
I've used abilon as a portable program and it seems to work fine.
Quote from http://www.portablefreeware.com/?c=2&sc=1
Create an empty subfolder called UserData in the application folder so that settings will be written locally instead of the user profile folder.
So Abilon is fully portable
In case you don't already know, Thunderbird can read RSS news feeds flawlessly.
Quite true on Thunderbird. Though I prefer Sage in Portable Firefox.
Sometimes, the impossible can become possible, if you're awesome!