While doing a search of the whole thread on the 'All' page using Ctrl-F in your browser works for shorter threads, I'm not surprised there isn't a visible 'All' link for long threads, and I'd bet Gnif isn't too happy with users manually adding /?all to long thread URLs due to the server load.
I really wouldn't advise it on the 360 pages of Batteriser thread:
https://www.eevblog.com/forum/blog/eevblog-751-how-to-debunk-a-product-(the-batteriser)/Also how many embedded Youtube videos in one page does it take to crash your browser? The [Print] button is somewhat safer as it strips images and videos so you only get the text for a local search.
However in the interests of being kind to the server, I would strongly recommend trying Google first as I suggested earlier. Its also better for you as although its a little more work, you can do more powerful searches than a Ctrl-F local search which will only look for exact matches (+/- case sensitivity).