The input options toolbar is located directly below the input bar textbox. Each option is a link that. Each image is from the Pastel Blue skin. Some of these features can be done from command. Each of these options may be removed in preferences, under the Input bar section of the General Tab.
Opens up a bar showing all the smilies that an account has set. Clicking one of them closes the bar, and adds the text for the smilie into the input bar textbox.
Opens up a bar showing the 15 colors that mIRC Color Codes allows. Clicking on one color makes the foreground (text) color change to the color that was chosen.
Translates text to another language for the user. It can either change the language of your output (in the input bar textbox shown in top image of the page) or your the input (in the chat pane). This can be done using the commands /translateme <language> for your output and /translatethem <language> for your input.
Mibbit includes a basic pastebin service for those who need it. The pastebin area opens up over the chat pane, so make sure to copy any text before opening it up. It tries to do syntax highlighting, even with pastes that are not code. Results vary wildly with it. When done, it puts a link into the input bar textbox. Can be opened with the /pastebin.
Mibbit also includes a basic file upload mechanism. The upload area opens up over the chat pane. There is a limit of 2MB for the file, though it can be of any filetype. When done, it puts a link into the input bar textbox. Can be opened with the /upload command.
Need a long url to be only a few characters? Mibbit also allows a quick version for this too. Put in a link, and it'll put in a (hopefully) shorter URL in the input bar textbox. Can also be done with the /minify <url> command.