opera /usr/share/doc/euphoria/search.html
If this doesn't work for you, replace opera with the command line name for your browser. Type in some Euphoria command into the search bar and the search functionality does not work.
The work around is to simply decompress the js files. Like so:
sudo gzip -d /usr/share/doc/euphoria/js/*.gz
Things ought to work out of the box though!
The resolution is to release 4.0.6 with search already decompressed in the deb package.
GitHub