I would also recommend what Kendo said, that you try turning your phone off and on, which like a computer, can help a phone behave better if it’s acting up. If it’s possible to remove your battery as well, this is also a good thing to try as it helps ‘reset’ things, but does not actually reset your phone’s settings.
In regards to the search engines, I’m not quite sure what you’re referring to regarding using the Google search engine on other browsers? Unfortunately Internet Explorer and Safari don’t always work as well as Firefox and Chrome. Since you said that using the Chrome browser allows you to login to the Parkinson’s UK forum I would recommend that you just use that.
Also, you could also try resetting your password and saving it in your internet browser. Sometimes the browser may have an older (incorrect) password saved.
Hope this helps!