Yes there are things that Firefox does better than others, and that is one reason I use Firefox. But there are definitely things I would like to see improved, like:

- PWA support on Linux

- better performance

- devtools should be able to handle sites with large amounts of js with sourcemaps

- fix a number of bugs that have been open for a long time

- don't lag behind standards as much (I'm not talking about things where they intentionally don't implement problematic "standards" pushed by google)

- make it feasible to embed gecko in other projects similar to how chromium is used by electron and webkit is used in "webviews"