I recently made my first Firefox extension and was surprised how simple it actually was (just for personal use: I had to repeatedly copy lots of data which I already had in a spread sheet into a web form - the extension lets you copy a whole row of data from the sheet and paste in into consecutive form fields on the website). As usual, it's not clear whether it was actually less work to develop the extension than it would have been to just manually put in all the data, but it was definitely better for my mental health.
Perhaps I will look into developing more serious extensions in the future, it was actually a quite pleasant experience.
Is it fair to say that developing extensions for Chrome is comparable?
For extensions which primarily add functionality to a target site, you can usually run the exact same extension code in Chrome, Firefox and Safari.
The latter two have API differences from Chrome - e.g. using the `browser` namespace for extension APIs instead of `chrome`, and Promises instead of callbacks for async functionality - but for the sake of compatibility they also implement Chrome's version of these APIs [1][2], so if you just use the Chrome APIs and don't venture into the more browser-internal APIs such as bookmarks, the same extension code will likely run everywhere, with some specific differences/incompatibilities noted in the docs below.
If you were to create a new cross-browser extension today, one of the main issues would be that Chrome Web Store no longer accepts new MV2 extensions so you have to use MV3 for it, but MV3 in Firefox currently has some serious usability issues around permissions which are being addressed in upcoming releases [3] so you'll want to use MV2 for it, however this likely just means you'd need to have separate MV2 and MV3 manifest.json files which get bundled into different zip files for submission to the different browser extension stores. I had to do this recently for one of my extensions [4]
Perhaps I will look into developing more serious extensions in the future, it was actually a quite pleasant experience.
Is it fair to say that developing extensions for Chrome is comparable?