You might find that using Google to search the forum is more helpful. In Chrome, for example, you can set up custom search providers in Settings > Manage Search Engines.
For “Search engine”, give it a helpful title like “Dorico Forum”.
For “Keyword”, type something you want to type into the address bar as a prefix for searching the forum: I went for “dorfor” (not something I’m likely to type by accident)
And for “Url with %s in place of query” I specified:
https://www.google.co.uk/#safe=off&q=site:www.steinberg.net/forums/viewtopic.php?f%3D246%20%s
Once you’ve added this, you can type e.g. dorfor “page up” into the address bar of your browser, and Google will search just this forum for the exact words “page up”. Hope this helps.