A macro could certainly be written, but an almost
equally easy way to search, which I use all the time
is, to give a bookmark a one letter nick, for example
for Google a bookmark
bookmark:
http://www.google.com/search?num=100&q=%s
nick: g
where %s represents the keyword, and writing
g yourkeyword
into the URL bar, then pushing Enter will start the search.
That can be done for every chosen search engine, with
a given nick in the bookmarks. Instead of CTRL + g
you only write one additional letter into the URL bar.
Fred