Not according to the KnowledgeBase article: https://support.mozilla.org/en-US/kb/enjoy-clutter-free-web-pages-reader-view And I didn't see mention of one here: https://support.mozilla.org/en-US/kb/keyboard-shortcuts-perform-firefox-tasks-quickly

Need feature request?

See: *[https://bugzilla.mozilla.org/show_bug.cgi?id=1144749 bug 1144749] - Create reader mode keyboard shortcut *[https://bugzilla.mozilla.org/show_bug.cgi?id=1160848 bug 1160848] - Add shortcuts to scroll to next/previous paragraphs in Reader Mode <i>Please do not comment in bug reports<br>https://bugzilla.mozilla.org/page.cgi?id=etiquette.html</i> You can vote for a bug to show your interest<br>https://bugzilla.mozilla.org/page.cgi?id=voting.html

Thanks, I voted.