I don't have LR associated with any type of file extension. Not one file type extension has Lightroom associated with it and I have both LR 5 and 6 installed.
All image type files are associated with Photoshop or the Windows image viewer (whatever MS calls it), not LR.
Actually LR is not for Opening image file unless you have already imported them into the catalog. I guess if you wanted to you could associate those file types to LR so when they are double clicked the Import dialog window open so you can import them into LR. But AFAIK that isn't the norm. YMMV