Just two personal experiences of why the quality of Firefox is far from Chromium's: downloads, and creating an extension.
A few years ago, they changed their interface for downloading. This introduced more than a dozen of bugs. Some were cosmetic, e.g. hover was the same color as foreground. Some were rare but caused a file loss. Some were performance related, e.g. deleting the history of downloads could take a minute with no visible change until the end. Most of these regressions are now fixed, but that made me lose confidence in the quality of Firefox.
This year, I had to develop a cross-platform extension for Chrome and Firefox. I started using Mozilla Documentation Network, but many pages seemed unmaintained. The relationship with extensionworkshop.com is unclear. The status of manifest v3 is poorly documented (most pages are for v2 only). The page about the compatibility with Chrome is incomplete. After a few struggles, I switched to Google's documentation. Then I lost time and energy on a severe bug with the Firefox tool that publishes web-extensions: https://discourse.mozilla.org/t/webexterror-unsupported-file...
A few years ago, they changed their interface for downloading. This introduced more than a dozen of bugs. Some were cosmetic, e.g. hover was the same color as foreground. Some were rare but caused a file loss. Some were performance related, e.g. deleting the history of downloads could take a minute with no visible change until the end. Most of these regressions are now fixed, but that made me lose confidence in the quality of Firefox.
This year, I had to develop a cross-platform extension for Chrome and Firefox. I started using Mozilla Documentation Network, but many pages seemed unmaintained. The relationship with extensionworkshop.com is unclear. The status of manifest v3 is poorly documented (most pages are for v2 only). The page about the compatibility with Chrome is incomplete. After a few struggles, I switched to Google's documentation. Then I lost time and energy on a severe bug with the Firefox tool that publishes web-extensions: https://discourse.mozilla.org/t/webexterror-unsupported-file...