I use User Agent Switcher to easily switch from the default Mozilla user agent to Googlebot. It is very useful in seeing parts of the web page that are crawlable by Google so you would know which sections you want and do not want to hide.
Got a Firefox add-on that helps optimizing your pages? Post it here.
I found this, I didn't try it yes, but it seems interesting.
Quote:
Seoquake is a Mozilla Firefox extension aimed primarily at helping web masters who deal with search engine optimization and internet promotion of web sites. Seoquake allows to obtain and investigate many important SEO parameters of the internet project under study on the fly, save them for future work, compare them with the results, obtained for other, competitive, projects.
Read More...
Here's another tool for your browser, not really an addon, It is the Wordtracker free keyword suggestion tool. Not as good as the commercial tool but if your on a tight budget well it does the trick.