Add-on for Firefox and Flock

• ClickableNow Add-on (A simple Mozilla extension.)
• @troynt's Twitter Script (Many more features -- Greasemonkey required.) 

ClickableNow Add-on

This add-on is quick to install and completely hassle free. There are no preferences or settings. Just install and go.

After the installation, when you visit a Twitter profile, look for the ClickableNow icon in your browser status bar. If you see the icon, pass your mouse over links on the background image.

Download Now 

@troynt's Twitter Script

In addition to clickable backgrounds, this script includes Nested Replies, Custom Search Tabs, Autocomplete, Pagination, RT button, Media Embed, URL Expansion, Hash Tag Search Links, and Social Links.

Install from userscripts.org