Change font size and font type of text-only mails in gmail webinterface

Problem:
Writing emails in gmail webinterface using the 'plain text' option results in wrong aligned text because gmail uses a non-fixed-width font.
Additionally some forwarded mails are displayed very small.

Steps to reproduce the 'very small font' effect:

• Write mail with 'plain text' option in gmail.
• Send mail.
• Receive mail with stand-alone mailclient, e.g. Thunderbid/icedove,
• configure client to compose mails in html/rich text mode
  ( Edit|Account settings|Composition&Addressing|Compose messages in HTML format (Icedove 3.1.16) )
• Forward mail to gmail account
• View mail in gmail webinterface.

Solution:
Found a userscript which sets the font in gmail to the browsers default monospace font. No further configuration needed.
The script can be found on userscripts.org - Gmail Fixed Font or directly downloaded from GitHub - jparise / gmail-fixed-font.

• Chromium pops up an install notification. Userscripts are directly supported. Browser restart seems to be needed after install to apply changes to the gmail webinterface display style.
• Firefox needs an extension to be able to handle userscripts. Greasemonkey can do that. Get it here (installation of the greasemonkey extension needs a browser restart). Now greasemonkey pops up a notification when clicking on a userscript and asks for installation. Reload gmail tab to apply display changes made by the script.

See the following screenshots for the difference. Take a look at the mail text for additional information.

Default gmail display settings:

The composed mail.	The same mail forwarded with an external email client set to html mail-formatting back to gmail.

This time with the userscript 'Gmail Fixed Font' enabled:

The composed mail like above.	The forwarded mail like above.

(Btw: It will be listed in the extension tab in chromium.)
Tested with chromium 15.0.874.121 (Developer Build 109964 Linux) Debian wheezy/sid and
Firefox 8.0 with Greasemonkey 0.9.13.
'Gmail Fixed Font' version 1.23 in both cases.

edit: (25.12.11)
- added install information for chromium and firefox.