Whenever I restart my Mac (iMac running Mojave 10.14.3) Thunderbird opens as a download instead of just being able to use from the Dock. This is driving me up the wall. If I try downloading another copy it just adds it as an alias. I have one copy of Thunderbird with a black arrow pointing towards it from the lower left in my Applications folder. It all works fine, but if I have to do a restart there is just a faded ? on the Dock where Thunderbird should be. In Applications there is then a small white rectangular icon saying Thunderbird, and if I click on it opens as if you have just down loaded it on the desktop with The Thunderbird image in a dialogue box with the arrow telling you to put it in applications and it opens as a new Application when you click on it in Applications. The Thunderbird Disk Image (Installer) icon is on my desktop, however, if I eject it then says quit the App as, it is in use. If I then Force quit Thunderbird and eject the Installer it totally removes Thunderbird. I have used Thunderbird on PC's in the past for years and have used it on my Mac's for the last 10 years with no problems and am experienced with adding new versions or installing old ones (as I prefer the one with colour in the tabs) and not the boring newer versions which are drab in comparison. I have tried installing the latest version, but the same problem occurs as described above.