web/extension: Correct the version used for the Firefox extension

[evilpie]

The version numbers must strictly equal one of those in these lists:

• https://addons.mozilla.org/api/v5/applications/firefox/
• https://addons.mozilla.org/api/v5/applications/android/

[evilpie]

Aside: For some reason the latest public version uses 48.0 and not 84.0 on desktop? https://addons.mozilla.org/api/v5/addons/addon/ruffle_rs/versions/0.1.0.1051/. Probably doesn't matter, both versions are incredibly outdated.

[torokati44]

Aside: For some reason the latest public version uses 48.0 and not 84.0 on desktop? https://addons.mozilla.org/api/v5/addons/addon/ruffle_rs/versions/0.1.0.1051/. Probably doesn't matter, both versions are incredibly outdated.

I think this is because "84" was also taken as invalid, and this could be some sort of built-in fallback for that case...?