modifying searchbar-textbox if specific search engine is selected

[marco]

Ciao all,

I have added a new search engine to Firefox following the
OpenSearch standard, all good.

If user then selects that engine as current one, I would like
to modify the default behavior of searchbar-textbox in relation
to the execution of the search. That is, after user has entered
some text in the textbox, he can then execute the query either by
pressing Enter or by left clicking the mouse on the magnifying
glass icon inside the textbox. In both cases, I would like to
perform some tasks before the search is executed, i.e. before
browser is redirected to the search URL.

Which event / attributes of the searchbar-textbox do I have to
customize? I tried with "textentered" and "keypress" with no
success.

Thanks a million forany hint / help.

marco