PLEASE HELP! Google search links redirect me to Ads and other websites!

So I just got this computer three months ago, about the second month it began redirecting me from google search links to other ad sites, search sites, and just random sites I did not want, I could not find anything to fix it, I stopped using it, then I took it to get repaired from where I bought they said they did not find anything, I am completely helpless I bought this computer for college which I'm about to start in August 24, but what is it good for if it can't go trough a simple google search, I do not have the money to buy a new one and my warranty has expired, it started out fine, I don't why this is happening.
It is also starting slowly, sometimes it won't even start, and everything takes a while to open.
I use Firefox as my browser, the latest version, I have Mcafee security center, It's a Dell X, I just don't know what to do, I hope I can get help here.
I followed the eight steps, did everything as well as I could cleaned my system twice etc. I am not computer savvy at all so bear with me.
Attachments are attached, please tell me if you need any more information.