Note that the *browser* findbar in Firefox uses "Title Case" for the labels, and it thus seem like a good idea to ensure that `PDFFindBar` in consistent with that.
Furthermore, the new label added in PR #13261 uses the "Title Case" format which means that currently the default viewer findbar looks inconsistent.
*Please note:* Based on the official Firefox localization docs, see https://firefox-source-docs.mozilla.org/l10n/overview.html#string-updates, changing only the casing should *not* require updating the key:
> 1) If the change is minor, like fixing a spelling error or case, the developer should update the en-US translation without changing the l10n-id.
Most of the files in this folder (except for the en-US folder) have been
imported from the Firefox Nightly branch;
please see https://hg.mozilla.org/l10n-central. Some of the files are
licensed under the MPL license. You can obtain a copy of the license at
https://mozilla.org/MPL/2.0.
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