Congratulations! bibtexbrowser is correctly installed!
Now you have to pass the name of the bibtex file as parameter (e.g. bibtexbrowser.php?bib=mybib.php)
You may browse:

Fatal error: Uncaught Error: Call to a member function contains() on null in /var/www/html/bibtexbrowser.php:3064 Stack trace: #0 /var/www/html/bibtexbrowser.php(2961): Dispatcher->key() #1 /var/www/html/bibtexbrowser.php(3106): Dispatcher->Dispatcher() #2 {main} thrown in /var/www/html/bibtexbrowser.php on line 3064