Tweak

Updated again: the extensions list, and the summary below, was last updated 2007-06-08, taking into account the new Addons site. Lots of sleazy spyware toolbars were finally removed. Added a few corrections based on comments here at 2007-06-17. Added a few more correction at 2007-07-29. Thanks!

Updated: the extensions list, and the summary below, was last updated 2006-12-09, taking into account the Firefox 2 release that made some extensions obsolete. Firefox out-of-the-box is catching up to Opera

Based on initial research from Dodd in the my.opera.com forums, I've compiled a list of the Top 150 most popular Firefox extensions, and classified the availability of the functionality they offer in Opera.

extensions.html

Some extensions are Firefox-specific (only relevant for managing Firefox itself), and there is considerable overlap in functionality for several extensions. That leaves the following summary:

• 41 extensions offer out of the box functionality in Opera 9, with roughly equivalent capability,
  
• 13 extensions are available by installing a UserScript or a Widget or dragging a button,
  
• 17 extensions require advanced customization or are only partially available,
  
• 45 extensions are not available at all in Opera.
  

[updated]After the December 3, 2006 update, out of 96 sets of extensions:

• 32 (sets of) extensions offer out of the box functionality in Opera 9, with roughly equivalent capability,
  
• 11 (sets of) extensions are available by installing a UserScript or a Widget or dragging a button,
  
• 13 (sets of) extensions require advanced customization or are only partially available,
  
• 40 (sets of) extensions are not available at all in Opera,
  
• 3 extensions are are Firefox specific (like dictionaries).
  

[updated again]After the July 29, 2007 update, out of 113 sets of extensions:

• 38 (sets of) extensions offer out of the box functionality in Opera 9, with roughly equivalent capability,
  
• 14 (sets of) extensions are available by installing a UserScript or a Widget or dragging a button,
  
• 21 (sets of) extensions require advanced customization or are only partially available,
  
• 38 (sets of) extensions are not available at all in Opera,
  
• 4 extensions are Firefox specific.
  

Corrections are welcome, but only from people who have actually studied both the extension and Opera's behavior. 'why would I need it' is a valid reaction to some extensions, but will probably not lead to changes in the table