[grid] fix bug in downloading files by ensuring browser vendor option…

[titusfortner]

Description

If browser vendor options missing, merge in mutable capabilities with the capabilities set.
I think this is better than casting the capabilities to MutableCapabilities to add it?

Motivation and Context

Not all bindings create an empty browser vendor options map by default

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (d810ac9) 56.49% compared to head (2a2369a) 56.49%.
Report is 10 commits behind head on trunk.

❗ Current head 2a2369a differs from pull request most recent head 3073c31. Consider uploading reports for the commit 3073c31 to get more accurate results

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Additional details and impacted files

@@           Coverage Diff           @@
##            trunk   #13024   +/-   ##
=======================================
  Coverage   56.49%   56.49%           
=======================================
  Files          86       86           
  Lines        5255     5255           
  Branches      187      187           
=======================================
  Hits         2969     2969           
  Misses       2099     2099           
  Partials      187      187           

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[diemol]

Where is the bug? In the absence of browser options key or the casting? In theory ofNullable should be handling it.

[titusfortner]

If there isn't a moz:firefoxOptions key, then we're just mutating a new hash that isn't attached to anything. Python downloading doesn't work unless another geckodriver option happens to be set.

[diemol]

Thank you for the explanation

[titusfortner]

What, the description made complete sense in my mind... 😂

I'll fix the formatting.