Auto merge of #20586 - emilio:moz-gradient-pref, r=xidorn
Auto merge of #20586 - emilio:moz-gradient-pref, r=xidorn

style: Respect the -moz- gradient pref again.

This hopefully allows us to unship them eventually.

Bug: 1451874
Reviewed-by: xidorn
MozReview-Commit-ID: 2MDRZLmLMM0

<!-- Reviewable:start -->
---
This change is [<img src="https://reviewable.io/review_button.svg" height="34" align="absmiddle" alt="Reviewable"/>](https://reviewable.io/reviews/servo/servo/20586)
<!-- Reviewable:end -->

avadacatavra/servo,DominoTree/servo,jimberlage/servo,SimonSapin/servo,jimberlage/servo,canaltinova/servo,splav/servo,avadacatavra/servo,pyfisch/servo,notriddle/servo,mbrubeck/servo,dati91/servo,splav/servo,jimberlage/servo,larsbergstrom/servo,szeged/servo,upsuper/servo,paulrouget/servo,ConnorGBrewster/servo,mattnenterprise/servo,notriddle/servo,saneyuki/servo,KiChjang/servo,jimberlage/servo,KiChjang/servo,paulrouget/servo,DominoTree/servo,SimonSapin/servo,canaltinova/servo,SimonSapin/servo,paulrouget/servo,SimonSapin/servo,upsuper/servo,peterjoel/servo,pyfisch/servo,cbrewster/servo,paulrouget/servo,pyfisch/servo,nnethercote/servo,larsbergstrom/servo,saneyuki/servo,ConnorGBrewster/servo,ConnorGBrewster/servo,nnethercote/servo,mbrubeck/servo,saneyuki/servo,jimberlage/servo,canaltinova/servo,ConnorGBrewster/servo,saneyuki/servo,pyfisch/servo,ConnorGBrewster/servo,notriddle/servo,nnethercote/servo,szeged/servo,KiChjang/servo,DominoTree/servo,sadmansk/servo,splav/servo,mattnenterprise/servo,sadmansk/servo,pyfisch/servo,cbrewster/servo,pyfisch/servo,cbrewster/servo,dati91/servo,dati91/servo,emilio/servo,nnethercote/servo,dati91/servo,saneyuki/servo,szeged/servo,splav/servo,peterjoel/servo,larsbergstrom/servo,avadacatavra/servo,splav/servo,canaltinova/servo,peterjoel/servo,notriddle/servo,KiChjang/servo,mbrubeck/servo,szeged/servo,emilio/servo,emilio/servo,larsbergstrom/servo,mattnenterprise/servo,splav/servo,SimonSapin/servo,emilio/servo,jimberlage/servo,paulrouget/servo,nnethercote/servo,splav/servo,mbrubeck/servo,szeged/servo,saneyuki/servo,KiChjang/servo,mattnenterprise/servo,larsbergstrom/servo,SimonSapin/servo,emilio/servo,peterjoel/servo,szeged/servo,splav/servo,peterjoel/servo,DominoTree/servo,sadmansk/servo,saneyuki/servo,SimonSapin/servo,sadmansk/servo,nnethercote/servo,upsuper/servo,paulrouget/servo,avadacatavra/servo,canaltinova/servo,splav/servo,larsbergstrom/servo,DominoTree/servo,peterjoel/servo,cbrewster/servo,larsbergstrom/servo,KiChjang/servo,upsuper/servo,notriddle/servo,saneyuki/servo,szeged/servo,emilio/servo,DominoTree/servo,mattnenterprise/servo,cbrewster/servo,splav/servo,larsbergstrom/servo,SimonSapin/servo,ConnorGBrewster/servo,sadmansk/servo,notriddle/servo,szeged/servo,pyfisch/servo,KiChjang/servo,DominoTree/servo,KiChjang/servo,pyfisch/servo,notriddle/servo,avadacatavra/servo,cbrewster/servo,canaltinova/servo,paulrouget/servo,jimberlage/servo,cbrewster/servo,DominoTree/servo,peterjoel/servo,paulrouget/servo,upsuper/servo,upsuper/servo,avadacatavra/servo,dati91/servo,larsbergstrom/servo,emilio/servo,dati91/servo,mattnenterprise/servo,peterjoel/servo,pyfisch/servo,mbrubeck/servo,sadmansk/servo,ConnorGBrewster/servo,szeged/servo,ConnorGBrewster/servo,nnethercote/servo,saneyuki/servo,avadacatavra/servo,mbrubeck/servo,DominoTree/servo,emilio/servo,peterjoel/servo,szeged/servo,nnethercote/servo,pyfisch/servo,dati91/servo,KiChjang/servo,mattnenterprise/servo,notriddle/servo,sadmansk/servo,mattnenterprise/servo,canaltinova/servo,emilio/servo,avadacatavra/servo,notriddle/servo,peterjoel/servo,jimberlage/servo,nnethercote/servo,canaltinova/servo,mbrubeck/servo,cbrewster/servo,mbrubeck/servo,emilio/servo,saneyuki/servo,KiChjang/servo,jimberlage/servo,dati91/servo,paulrouget/servo,notriddle/servo,paulrouget/servo,upsuper/servo,DominoTree/servo,sadmansk/servo,larsbergstrom/servo,upsuper/servo,nnethercote/servo