When "Start" recording is on, then in Firefox Portable (beta) all links become untrusted "Get me out of here" warnings.
In the Jaksta Media Recorder settings James - not in the FF settings.
I could not follow the instructions and don't see the tabs/options you referred to. Attached wit what I see under exceptions. Could not find "HTTP Tab and click the Reinstall Firefox HTTPS monitor"
Sounds like the certificate has not been added to the store to allow SSL scanning.
You can either turn off ssl scanning or reinstall the cert
Settings > Internet Downloads
Switch off Monitor HTTPS/SSL
Settings > Internet Downloads > Advanced button
HTTP > Reinstall Firefox HTTPS Monitor
Here are some FAQ's that may help as well