This is currently not possible with WebExtensions. WebExtensions is currently significantly less effective than other types of Firefox add-ons . Although the features available for WebExtensions add-ons will improve over time, it is expected that WebExtensions will remain less capable than other types of add-ons. The fact that WebExtensions will be less able to modify Firefox is one of the reasons Mozilla is moving towards WebExtensions. They are considering reducing the potential of extensions to modify Firefox as useful for several reasons. First of all, they mentioned that this would make it easier for them to change the internals of Firefox without breaking add-ons .
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