SUMMARY
Search for files in the file upload window.

I am sure there is a way to alter the default configuration for the window called by Firefox so that it offers the ability to search. I don't know how to do it yet, but for future releases could you please add that functionality by default?

STEPS TO REPRODUCE
1. Change Firefox default file manager to Dolphin
2. Click on 'upload file' on a website
3. Try to see if you remember exactly where and when the file you are uploading is. 

OBSERVED RESULT
There is no in window way to alter the configuration. It does not take a cue from the global defaults either.

EXPECTED RESULT
Be able to search for a file to upload, something Windows actually gets right.

SOFTWARE/OS VERSIONS
Kubuntu 18.10
Plasma 5.50.0

ADDITIONAL INFORMATION
I never actually noticed this as missing since I rarely used Windows, but the user requested this functionality and I was surprised to find it was neither easy to find nor could I find other people talking about it.