The reason Joplin’s Web Clipper is useless for this is because the URL NewsBlur is showing doesn’t reference the article being shown. The NewsBlur team could fix this by updating the URL as articles are being viewed, e.g. change:
https://www.newsblur.com/site/:<id>/<site-name>
to something like this (for a link back to a specific article in NewsBlur):
https://www.newsblur.com/site/:<id>/<site-name>#<article-id>
…or even better, include a link to the target article, as a favor to other developers:
https://www.newsblur.com/site/:<id>/<site-name>#<article-id>/<url-encoded-article-link>
Then Joplin Web Clipper’s “Clip URL” would work as expected. Clip Selection already works, but seems useless since it doesn’t capture the URL.
Another approach that doesn’t require the benevolence of the NewsBlur team would be to create an RSS Clipper browser plugin. That would use the Joplin Data API to barf a link to the current article being displayed into Joplin. That link is available to browser plugins via the article HTML:
#story_pane > div.NB-story-pane-container > div.NB-feed-story-header > div > div.NB-feed-story-title-container > a
A plugin could also allow selecting a target subfolder, adding optional note text, checkboxes to include the article URL, the NewsBlur site URL, the RSS description, etc.
The same UI could also support Obsidian or others. And no reason this plugin couldn’t support other RSS readers, since it’s just culling elements from a webpage.
Downsides? It’s two plugins, one for Mozilla, another for Chrome. And it would need to be maintained, since it’s parsing the NewsBlur current article page for HTML IDs that are subject to change.