When I click on Choose Tags straight from the new post form, the window with blue overlay opens, but the window disappears and only the blue overlay stays.
The Choose Tags window opens normally when submitting the post with the Post Discussion button.

    caolan
    Tried to replicate in an updated firefox, in budgie, three times. specs: ancient thinkcentre.
    Could not replicate; window opens and stays intact.
    Could be a ton of factors here.

        brent Just restarted, updated system, Gnome-shell, Firefox. Still the same result.

          I got this with my phone, but never on my computer.

          caolan When I click on Choose Tags straight from the new post form, the window with blue overlay opens, but the window disappears and only the blue overlay stays.

          I can confirm that. In normal, not maximized Firefox window Choose Tags dialog opens and immediately disappears:

          Choose Tags dialog does not disappear in maximized Firefox window:

          Edit: Choose Tags disappears in not maximized Firefox window in all DEs - Plasma, Gnome, Mate, Budgie.

            You should file this with the Flarum developers.