luckily for me my credit card, banking etc sites work on linux/firefox/chrome etc... if you have website specifically asking for IE then you can install plugins/addons for Firefox to spoof the "user agent" to send IE as the agent to the website so it thinks you are browsing with IE... but use at your own risk.... who knows if a bug in FF or the banking website causes you to empty all your deposits
well there is no alternative of activex if a web based service use that.
I am a full time linux user, the same problem of some on-line payment sites are not properly working with firefox (including in Windows). I am also forced to use IE using wine so that to avoid the problem of activex.
It would be nice if we have a list of good, bad, and ugly sites that are of day-to-day utility such as banks, payment gateways, etc., in term of their being agnostic towards operating systems / platforms and browsers.