I am new here so hoping I am in the right place. Upgraded (ha) to Mojave yesterday. Since then I have lost capability of opening any folders or files or documents with double click. Must right click to "open" and that is it. It has also messed up my thunderbird mail. First cuomer service from Apple tried to help and couldn't and the second person had NO idea what he was doing and in fact after 3 hours had my computer really messed up. Anyway, have gotten everything back in order but still have the original problem. Was told the only way now is get rid of Mojave but have to back up entire computer because it could gt lost going back to Sierra. Apple guy said to get a 3 terabyte hard portable drive (about $800) before doing that. I am a disabled vet so if I had that money i would just get a new computer heck. Am at my wits end...any suggestions or ideas would be greatly appreciated.