I have used Google Chrome (before I understood what privacy was) and a variety of Chromium-based browsers (mainly Brave, but also Vivaldi, Ungoogled Chromium, ...) for a long time. However, since I switched to Linux at the end of last year, I stuck with the Firefox (that came pre-installed with Ubuntu). Although I also installed Brave, a nostalgic part of me wanted to experience what Firefox was like after years of Chromium loyalty (I did use Firefox for some time when I was around seven or eight).

Since switching, Firefox has served me reasonably well, and despite a few RAM spikes here and there, I have almost no reasons to complain. Almost. Firefox, while it does almost all things better than Chromium browsers, does miss quite a few small features that I missed while using the browser. Here is a list of those features (not exhaustive, and I might discover more in the future).

1. No extension grouping. Google Chrome has a fantastic configuration that allows you to group all the extensions under one single icon in the toolbar (Brave seems to do this out of the box). Firefox, on the other hand, has no such features. As someone who around 20 or so extensions at any time, you can imagine how the toolbar must look like.
2. No way to add custom detect search engines. Google's Omnibox detects search bars from any websites that I visited and added them automatically in the search settings. And if I wanted to, I could go to the settings and add them to the main search engine list and/or assign custom shortcuts to each of them. Firefox does not allow me to do this from the Awesome Bar (pretty cringe name too). Instead, I have to add the "search bar", which might detect the search engines and let me add them. Firstly, why can't I do this from the address bar itself? The search bar has literally no utility for me other than this tiny but lifesaving feature. Secondly, this is a hit-and-miss thing. Many prominent search engines like DuckDuckGo is not detected by Firefox as search engines to be added. Granted, it is already among the default options, but still, and this brings me to... thirdly, there is no way to delete the shortcuts that have been assigned to the custom search engines. For example, @duckduckgo is DuckDuckGo's shortcut. I'd never need or type such a lengthy thing, so I wanted to delete it and add @ddg instead. Nope, not happening; Firefox will only let me add new shortcuts and not delete the default ones. The only way to do so would be to remove the entire search engine and add it manually, which is not possible in DuckDuckGo's case. Therefore, the only thing that is possible seems to be adding extensions, which is one more step that I did not need (but had to do so anyway).
3. No tab grouping. Granted, this is not actually present in Chrome itself, but is an offering by Vivaldi, a Chromium-based browser. This should be very simple to do for Firefox, presumably, and would be a fantastic thing for people like me who have numerous tabs, related to different topics, open at any time. I couldn't even find any extension that offered this feature; all seemed to push me towards a tab tree thing, which I did not prefer.

As of this moment, I can only think of these three features. It is possible that I might have run into more inconveniences, but these are all I can recall at the moment. Hopefully, some day, Mozilla will finally port these features over to what is otherwise a fantastic browser.