Option to run arbitrary JavaScript on startup

[unappendixed]

I am using custom actions to synchronize the native tab bar with my vertical tab panel (so that when Sidebery, my vertical tab extension, is active, the native tab bar is hidden, and vice versa) but I always need to hit the key I've bound that to get them in sync after a restart. It would be fantastic if there was a flag in about:config where you could input a string to be eval'd in the top browser context when Floorp launches. Then I could just set the 'hidden' attribute on the native tab bar to be opposite whatever the state of the sidebar is.

And, of course, I've just somehow overlooked this feature and it's been supported in Floorp forever then thanks and apologies lol.