Custom parameters are incorrectly incorporated into the Exec= line using Firefox

[BudgieInWA]

Using the "Custom parameters" field when editing a Web App causes an invalid Exec line in the resulting .desktop file using Web Apps 1.3.2.

1. Create a Firefox Web App for any website.
2. Enter something into the "Custom parameters" field (with no trailing space).
3. Save the entry and launch the resulting app from the applications menu.

The Firefox instance that is loaded does not show the configured website as expected.

The problem is that the custom param is concatenated with the space on the wrong side: Adding a custom param of $$$$$$ results in an Exec line ending like the first line, when it should be like the second:

--no-remote  $$$$$$"https://github.com"'
--no-remote $$$$$$ "https://github.com"'