Unfortunately, mobile web browsers like the iPhone, iPad, Kindle Fire Tablets, and Android Tablets don't support extensions like Planapple's Save Button.
On browsers that don't support the Save Button, you can still save web sites into your Planapple trip by copying the web address (URL) and then pasting it into the Add... web link option at the top of the Planapple notebook list. Or you can also add things directly to your trip from Planapple's Idea Finder tab.
We do have an older "bookmarklet" save button available, and you might be able to get this working in some mobile web browsers. See the Get the Save Button at Planapple's main site for details.
Note: The first time you use the Save to Planapple bookmarklet on a mobile device, it may take up to 30 seconds to load. Give it a chance -- it'll be much faster after that.
(And if you're curious, Wikipedia has more information on the general idea behind bookmarklets.)