Save form data after submit post

Will be great to save form data after submit post, because if exception will be thrown user can come back to the form and get text, save it locally, retry submit etc.

Steps to reproduce:
1. press "New post" button
2. fill post text in the form
3. press submit, that should throw server exception
4. after exception I have "Error 500" page and press back button in browser

Actual result: form is empty
Expected: entered text is saved