Neither Firefox nor it's add-ons should affect the computer settings.

You may have ad / mal-ware. Further information can be found in the Troubleshoot Firefox issues caused by malware article.

Run most or all of the listed malware scanners. Each works differently. If one program misses something, another may pick it up.

Type about:support in the address bar and press Enter. Under the main banner, press the button; Copy Text To Clipboard.. Then in the reply box at the bottom of this page, do a right click in the box and select Paste. This will show us your system details. No Personal Information Is Collected.

I know it's not malware, I clean my computer at least once a week. I forgot to add; I can have the power plan window open & then open Firefox & I can watch the plan switch.

UKBlue said

open Firefox & I can watch the plan switch.

Does it switch back?

FredMcD said

Type about:support in the address bar and press Enter. Under the main banner, press the button; Copy Text To Clipboard.. Then in the reply box at the bottom of this page, do a right click in the box and select Paste. This will show us your system details. No Personal Information Is Collected.

I've called the big guys to help you. Good luck.

I have to manually switch it back

A post was flagged as Solved Problem. Please remove that flag. If you don’t, others that can help may not read this post.

Not sure how that happened because I certainly didn't do it. How exactly do I go about unflagging something?

Go to the responce marked as "Solved Problem." To its left, and press the link there.

So you normally try to use Power Saver on your Windows 7 laptop and when you start a application like Firefox it increases load on system enough that it changes to Balanced ?

No: I usually run in High Performance, when I open Firefox is switches the plan to Balanced.