Text Area Resizer And Mover comes to the rescue; At least for Firefox users. The Firefox extension makes it possible to resize virtually any html form on the Internet. This is done in an uncomplicated manner.

Once a html form has been located that the user wants to resize he simply presses the right-mouse button after moving the mouse into the form. The mouse pointer changes to a resize symbol and the html form can be resized by moving the mouse.

The default html form at Ghacks for commenting on an article:

The altered html form at Ghacks:

It is possible to make it smaller or bigger although most users will probably stick with the latter. Text Area html forms are those that usually span across multiple rows. The extension cannot be used to increase the size of the Google Search form but as you can see in the images above it is possible to change comment forms and the like easily.

The forms only expand to the right and bottom of the screen but never to the left or upwards.

Update: The Firefox add-on has been discontinued. You can use the following bookmarklet instead.