In the job details page, you will see at your right, the GlassDoor icon.
Click on it, and you will then the company size.
If you don’t see the GlassDoor icon
In that case, click on the company name.
You will be redirected to the company details page. In the company details page, click on the “LinkedIn” icon.
Then, click on the concerned company, and see the company size: