I develop in Firefox and it’s pretty rare that I have to spend time on other browsers, which was not the case a decade ago.

It’s also not like Flash was perfect at this: I ran into compatibility issues where something worked on Windows but not macOS or vice versa, and the frictional cost of having an unstable, primitive IDE was significant — especially since Adobe typically ignored bug reports until the next major release, at which point they’d tell you that you should drop $500 for the privilege of seeing whether they’d fixed it.