Editing Entries

I have been using WP for about a month and a half, so I should have asked this question a while ago.
When adding/editing entry and say I want to bold text. I highlight the text, hit the “B” button and unfortunately, it adds the required tag at the bottom of what I wrote. Is this a default function or something qwerky with Mozilla Firebird? Can it add the tags around the highlighted text (eg like editing text in MS Word)? Thanks!