Let's keep it simple: you have to open several URL at once and you are wondering how to do that: let's find out together!
Open multiple URL
My favorite website is https://www.openmultipleurl.com/
The name is that clear, that it is easy tu read and understand: Open + multiple + URL. I thing they bought this for SEO purposes 😅
URL Opener at 10 Best SEO
This is the URL https://www.10bestseo.com/url-opener/. Maybe too many ads on this website, but you gotta find a way to earn enough for your work and server ;-)
Multiple URL Opener at Visiopark
I don't exactly know Visiopark, but I could tell that there website/tool is simple and good to use. http://www.visiospark.com/multiple-url-opener/
Bulk URL Opener
This is a full project: a website, some browser extension and an Open-Source project on GitHub. To access it, go to https://www.bulkurlopener.com/
Like the other ones "Open multiple URL" and "Bulk URL Opener" the name speaks for itself. Once again this is an EMD (Exact Match Domain) which first purpose is to better rank on Organic Results
Note: I don't use any extension like Firefox or Google Chrome extension, but that could also be an option!