I always record webinar with a web-based software calls Acethinker Screen Recorder, It is a free online tool that lets you record your screen right from the browser. And here are the steps to record webinar with it. Feel free to contact me if you have problem in it.
Step 1. Run your web browser and visit Acethinker Screen Recorder website, this app compatibles with IE, Firefox, Chrome, Safari, Opera, etc.
Step 2. Click 'Start' to open the screen recording app.
Step 3. Select the recording mode you like, Full screen record or Region record. I'd recommend the full screen mode for webinar recording.
Step 4. Click on the red button to start the screen recording.
Step 5. Once you stop the recording, you can click on "Show in folder" to find the recorded webinar.