Use /firefly prefix on local docs dev

[peterbroadhurst]

See #451

[codecov-commenter]

Codecov Report

Merging #461 (e8f40cf) into main (c1f9507) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #461   +/-   ##
=======================================
  Coverage   99.92%   99.92%           
=======================================
  Files         266      266           
  Lines       15101    15101           
=======================================
  Hits        15090    15090           
  Misses         11       11           

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[nickgaski]

LGTM. Adding baseurl: /firefly allows all links to resolve in #451 and persists a successful local build.