Describe the bug
When the pop-up signing dialog opens, resizing the window doesn't properly resize the UI.

To Reproduce
Steps to reproduce the behavior:

1. Request a signature from a dapp.
2. When the signing dialog opens, try to resize in.
3. Notice that the contents remain fixed in the middle of the window.

Expected behavior
UI resizes to fill the available space.

Screenshots

Browser details (please complete the following information):

• OS: Windows 10
• Browser: Firefox
• MetaMask Version: 4.17.1
• New UI

Additional context
This is particularly annoying when the dialog has enough information to trigger a scrollbar in the DATA section.