Here is more about SafeBrowser from the developers:
Use the SafeBrowser extension to browse the web safely. With this extension you can simply surf the web as you normally do, but when you get to a site you’re not sure you can trust…
1) Right click on the link to that site and open it using the “Open link in SafeBrowser” option in the drop down menu.
2) Click on the “Open page in SafeBrowser” menu option or browser button to view the page you are currently viewing in SafeBrowser, and continue surfing from there.
3) At any time you can click the “View Outside SafeBrowser” button to view the page you are currently looking at in a normal browser window. Note though that this button is disabled for sites categorized as SUSPICIOUS or HIGH RISK.
You can pick up the SafeBrowser add-on for Firefox at the Firefox Add-ons website.