If you use Gmail and Firefox web browser, this Greasemonkey script is fantastic.

Features of this script:
- Ads… GONE!
- Invites box… GONE!
- Warning when using chat to SMS… GONE!
- Invite after emailing a non-gmail user… GONE!
- Quicklinks are now active buttons
- Attachment icon will be more appropriate for type instead of paperclip for all (except with multiple differing attachments in a single message)
- Row Hover highlighting in blue
- New email highlighting in yellow
- Selected email highlight in light blue
- Show details for message by default
- Toggle Tango Icon theme for system folders/labels, top right nav bar, and refresh link
- Toggle visibility of GMail logo.
- Toggle showing of message details. Same as logo.
- Toggle automatic return to your inbox after replying to an email.
- Adjust font size without changing browser font/zoom level.
- Toggle footer visibility per line.