Don't check mic permission on Firefox

[imnasnainaec]

#3247 broke recording on Firefox:

Uncaught (in promise) TypeError: 'microphone' (value of 'name' member of PermissionDescriptor) is not a valid value for enumeration PermissionName.

(See https://stackoverflow.com/questions/53147944/firefox-permission-name-member-of-permissiondescriptor-camera-is-not-a-vali)

This fix checks for permission on all non-Firefox browsers and assumes permission for Firefox.

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This change is 

[codecov]

Codecov Report

Attention: Patch coverage is 66.66667% with 4 lines in your changes missing coverage. Please review.

Project coverage is 74.59%. Comparing base (92050a5) to head (3e60889).
Report is 36 commits behind head on master.

Files with missing lines	Patch %	Lines
src/components/Pronunciations/Recorder.ts	0.00%	2 Missing ⚠️
src/components/Pronunciations/utilities.ts	77.77%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3298      +/-   ##
==========================================
- Coverage   74.59%   74.59%   -0.01%     
==========================================
  Files         279      279              
  Lines       10680    10687       +7     
  Branches     1287     1288       +1     
==========================================
+ Hits         7967     7972       +5     
- Misses       2351     2352       +1     
- Partials      362      363       +1     

Flag	Coverage Δ
backend	83.87% <ø> (-0.03%)	⬇️
frontend	66.45% <66.66%> (+0.02%)	⬆️

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[jasonleenaylor]

Reviewed 3 of 3 files at r1, 1 of 1 files at r2, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @imnasnainaec)