Google Search -- site:addons.mozilla.org inurl:en-US/firefox/addon currency conversion
http://www.google.com/search?num=100&q=site%3Aaddons.mozilla.org+inurl%3Aen-US%2Ffirefox%2Faddon+currency%20conversion
Dcurrency (Status Bar shows 3 currencies, uses Yahoo Finance, specify delay)
https://addons.mozilla.org/en-US/firefox/addon/6462
Converter (converts measurements within page)
https://addons.mozilla.org/en-US/firefox/addon/2286
You can search Addons yourself by creating a keyword shortcut:
Name: addons: Search for extensions at addons.mozilla.org/firefox
Keyword: addons:
Location: http://www.google.com/search?num=100&q=site%3Aaddons.mozilla.org+inurl%3Aen-US%2Ffirefox%2Faddon+%S
Description: This is a Google search not the same as the one on the Search Bar for Addons
Name: addons:s Search addons.org with it's own search
Keyword: addons:s
Location: https://addons.mozilla.org/en-US/firefox/search?q=%s&status=4&show=50
Description: (create such shortcuts by right clicking on the search within an addons page)
More information on keyword shortcuts, see
Firefox Keyword Shortcuts
http://www.mvps.org/dmcritchie/firefox/firefox.htm
Questions such as yours are best asked in mozilla.firefox.support
where questions are answered by other users, rather than in
a developer newsgroup.
--
HTH,
David McRitchie, extensions I use are briefly documented on my site
Firefox Custom: http://www.mvps.org/dmcritchie/firefox/firefox.htm
correction: best asked in mozilla.support.firefox