You can absolutely either move or remove the prefix text from thread pages. It's an easy template edit. The template you want to open and edit is the THREAD_VIEW template. Just navigate to Appearance > Templates > thread_view and then make the following edits. These changes are limited to the first two lines of code.
Line 1 controls the actual title of the page that's visible up in the browser tab. So if you'd like to remove the prefix from the title entirely, change:
<xf:title page="{$page}">{{ prefix('thread', $thread, 'escaped') }}{$thread.title}</xf:title>
to
<xf:title page="{$page}">{$thread.title}</xf:title>
Basically, this is the prefix code you're either removing or moving:
{{ prefix('thread', $thread, 'escaped') }}
As you can see, it's in both lines 1 and 2.
For line 2 (the H1 title on the page itself), if you'd like to remove the prefix altogether, just remove the code I just displayed directly above. If you'd like to move the prefix from the front of the text to the rear, change:
<xf:h1>{{ prefix('thread', $thread) }}{$thread.title}</xf:h1>
to
<xf:h1>{$thread.title} {{ prefix('thread', $thread) }}</xf:h1>
When finished, click the Save button and you'll be all done.