I recently switched back from firefox to safari as my default browser, mainly because firefox is too big, slow and hangs from time which anoyed me more and more.
The switch became possible, because i found some extensions to safari, which counterparts i used on firefox excessively:
1.) the most important tool on firefox: Firebug, Safari 3.0 comes with a almost-feature-rich-firebug build in, as long you know the command line to activate it:
defaults write com.apple.Safari WebKitDeveloperExtras -bool true
then right-click on some element on the webpage and you will see the web developer tools window.
2.) add some extensions to safari:
Inquisitor 3: adds more searches to the google search field with livesearch and the possibility to extend the search field with custom searches like wikipedia, imdb, yahoo, … Has a very cool interface:
Delicious Safari: adds a delicio.us menu to safari, enabling posting bookmarks to your delicio.us account and to access all your delicio.us bookmarks from the safari menue (including tags and favorites)
Safari Tidy: adds a HTML validator to Safari, including highlight of errors and warning with line numbers in the source code view
Safari Microformats: to display a microformats icon in the location bar when the current page containes some microformats