Firefox keeps opening new tab and asking how to open file #78

Hi,

I installed the plugin for Firefox and try to open a database by double clicking in Windows Exlporer. When I do I get the pop-up asking me what to do with the file, open with Firefox or save. When I select Open with Firefox it opens a new tab and again gives me the pop-up with what I want to do. Every time I click open with Firefox this repeats itself, but the database is not opening.

And from looking at the options I should be able to start the plugin even without a database, how do I do that?
Edit: I just found this question in the FAQ, but unfortunately, it does not help. I have Firefox 53.0, which is not mentioned in the possible Firefox version (only 3 and 4 are mentioned). If I go to the web developer tools in the menu SQL Lite Manager is not listed.
firefox web developer menu

Thanks.