String fix for speed feature page [#14298]

[craigcook]

One-line summary

Change requested in https://github.com/mozilla-l10n/www-l10n/pull/381

Testing

http://localhost:8000/en-US/firefox/features/fast/

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 76.57%. Comparing base (7590b0e) to head (e976920). Report is 3 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #14313   +/-   ##
=======================================
  Coverage   76.57%   76.57%           
=======================================
  Files         144      144           
  Lines        7804     7804           
=======================================
  Hits         5976     5976           
  Misses       1828     1828           

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