Fantastic addon for desktop version of Firefox.

Suggestions/ideas for the future:

[01] A 'Preserve Speed' slidebar option. Self-explanatory: pitch can be changed without affecting playspeed.

[02] Dedicated behavior modifier functions (additive, multiplicative) for play speed and pitch, separately.

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As of this posting date, this addon exhibits the following issue in Firefox Beta (Android):

[01] Within the menu interface, switching the On/Off slider to 'ON' position reverts back to 'OFF' position upon exiting, as well as forcing the active page to reload.