Fix for Scrolling With Firefox Under Windows/Ubuntu

[Magnitus-]

... and some other edge cases.

Inspiration for the fix was drawn from this merge request in react-virtualized: bvaughn/react-virtualized#110

[codecov]

Codecov Report

Merging #7 into master will decrease coverage by 1.19%.
The diff coverage is 50%.

@@            Coverage Diff            @@
##           master       #7     +/-   ##
=========================================
- Coverage   92.85%   91.66%   -1.2%     
=========================================
  Files           3        3             
  Lines         140      144      +4     
=========================================
+ Hits          130      132      +2     
- Misses         10       12      +2

Impacted Files	Coverage Δ
src/constants.js	100% <100%> (ø)	⬆️
src/index.js	84.21% <25%> (-3.07%)	⬇️

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[clauderic]

Hey @Magnitus-,

Thanks for submitting this PR!

I'll try to set aside a bit of time to dive in and test this fix sometime today, but this looks great at a glance 👍

[Magnitus-]

Sure. Take your time, there is no rush. Let me know if you'd like any adjustments to the PR and thank you for this project. It's great.

[clauderic]

Thanks for this contribution @Magnitus-! Just had a few stylistic/linting nitpicks, but otherwise this is perfect.

Just shipped this fix with 2.0.5 🎉