optimize rules for Firefox on FirefoxOs

[mimmi20]

This PR optimizes the rules for firefox on firefoxos a bit.

[codecov]

Codecov Report

Merging #1994 into master will increase coverage by <.01%.
The diff coverage is 0%.

@@             Coverage Diff              @@
##             master    #1994      +/-   ##
============================================
+ Coverage     50.93%   50.93%   +<.01%     
  Complexity      905      905              
============================================
  Files          1697     1697              
  Lines         61186    61182       -4     
  Branches      26834    26850      +16     
============================================
  Hits          31165    31165              
+ Misses        30021    30017       -4

Flag	Coverage Δ	Complexity Δ
#full	45.86% <0%> (ø)	0 <0> (ø)	⬇️
#lite	2.1% <0%> (ø)	0 <0> (ø)	⬇️
#standard	26.91% <0%> (ø)	0 <0> (ø)	⬇️

Impacted Files	Coverage Δ	Complexity Δ
.../browsers/firefox-on-firefoxos/firefox-os-0-x.json	0% <0%> (ø)	0 <0> (ø)	⬇️
.../browsers/firefox-on-firefoxos/firefox-os-1-4.json	0% <0%> (ø)	0 <0> (ø)	⬇️
.../browsers/firefox-on-firefoxos/firefox-os-1-2.json	0% <0%> (ø)	0 <0> (ø)	⬇️
.../browsers/firefox-on-firefoxos/firefox-os-1-0.json	13.33% <0%> (+0.83%)	0 <0> (ø)	⬇️

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