As for speed... the standard Firefox browser was absolute dogshit. Hugged a lot of memory. Now on Opera and that's sweet as, never really bothered using that before.. but it seems very smooth and fast.
Maybe the distro-version of Firefox is older and you could use the latest version?
Chrome / Chromium (open source) is also widely supported and pretty fast (though not as slim as before) in case you encounter corner cases on Opera.
Having Linux on a laptop is a bit more work and can be a bit daunting/slower/buggy as you need more advanced features like power management, wifi etc. working correctly all the time. I run Ubuntu with XCFE on a stationary with 64GB RAM (will be Mint next time), so have less issues. We do use Linux on laptops for TV/browsing-usage as well.
Using Suspend at night and have session already running/waiting for next usage, so resuming usage is quick.
Hibernate (write to disk) sometimes crashes for me unfortunately, and is a feature you need to enable manually, but have used it to save my running sessions from ie. planned electric outages.
The advantage over several years now has been that my setup, once I've got it to work the way I need it, works stably without much need for much maintenance, random reboots, external interferences, obnoxious popups/indications or spying (hopefully). I try to keep current on security updates, especially for internet-using applications. On the occasional reboot/power outage, my computer auto-restarts, auto-logins, locks screen and starts everything I require to run again to boot.
It works so well my wife doesn't want Windows anymore on new computers (her previous Windows was Vista!

). For when we purchase new laptop, she wants me to either buy with Linux or install Linux on Windows-free computer. Installing Linux on her laptop has extended its life for many years already, and wouldn't work with Windows since it needed a reinstall that just wouldn't work.