update-alternative --config x-www-browser ?
another universal solution, save the following codes to a file,
Code:
#!/bin/sh
export MOZILLA_FIVE_HOME="/opt/firefox"
url="$1"
if [ ! "$url" ]; then
url="about :blank"
fi
if $MOZILLA_FIVE_HOME/mozilla-xremote-client -a firefox openURL\("$url",new-tab\); then
exit 0
fi
$MOZILLA_FIVE_HOME/firefox "$url"
exit 0
make the file executable, add the following line to pref.js in thunderbird's profile directory, be sure edit that file while thunderbird isn't running
Code:
user_pref("network.protocol-handler.app.http", "/path/to/that/file");