I do not think so. It was such a GOOD feature. Imagine opening your browser and you had all your news instantly in your bookmark under address bar. I loved Firefox for this.

But, thankfully, you can have almost the same thing with Livemarks extension.

Opera used to have a built in RSS reader that was better in my opinion.

Some of the people behind Opera has built Vivaldi, which also contains an RSS reader. I haven't used it myself, but it looks promising.

Seems risky to rely on a browser as your RSS reader. I know you could always export your OPML file but not every reader seems to import/export that spec correctly