Internet connectivity

I have been using Firefox for a number of years. I use it with Windows 10. My internet connectivity has recently degraded to the point it is no longer viable. It is painfully slow and I keep getting "time out' notifications. I contacted my service provider and they suggested using a different browser. Although I was skeptical, I installed Chrome on my machine and tried it. Connectivity is back to normal. Why? What happened to Firefox? It shows as being up to date. How can I fix it?