Preview will not stay as default viewer for jpg or pdf files

Hello,

I have a macbook pro and in the last few months, when I click on jpgs of pdfs or anything that I normally open in Preview, it will open in Photoshop Elements or a program called Grab. I have gone to open with and Preview is not even on the drop down list. I have to choose other and then select Preview from the main list. I can't count how many times I have had to do this. I have gone into Get Info and changed Open all similar files and it still doesn't stick. I will be able to open the jpg or pdf file that I have changed the settings for but not new files I save off the web or from emails. It happens in Firefox and Safari.

I like Preview and I want to continue to use it as my default viewer. Any suggestions? This problem has been happening in Sierra and now High Sierra.