Filling as a good first bug to learn workflows.

As the change is easy, it is mostly to learn how to contribute to Firefox.

To run the linter:
$ ./mach lint -l clippy testing/geckodriver/ --warnings

Warnings:

xxx/testing/geckodriver/build.rs
  45:12  warning  this `else { if .. }` block can be collapsed  clippy::collapsible_if (clippy)

xxx/testing/geckodriver/src/main.rs
   318:85  warning  redundant clone                 clippy::redundant_clone (clippy)
   481:53  warning  redundant clone                 clippy::redundant_clone (clippy)
   860:47  warning  redundant clone                 clippy::redundant_clone (clippy)
   933:38  warning  redundant clone                 clippy::redundant_clone (clippy)
   955:41  warning  redundant clone                 clippy::redundant_clone (clippy)
   965:41  warning  redundant clone                 clippy::redundant_clone (clippy)
  1677:61  warning  using `clone` on a `Copy` type  clippy::clone_on_copy (clippy)

Tutorial to contribute:
https://firefox-source-docs.mozilla.org/tools/docs/contribute/how_to_contribute_firefox.html

Please don't ask for the bug to be assigned. It will be automatically assigned to the first patch.

It looks like this has been fixed as part of bug 1807248.

$ ./mach lint -l clippy testing/geckodriver/ --warnings
✖ 0 problems (0 errors, 0 warnings, 0 fixed)