When I use Ctrl + Left/Right arrow to move from one word to another, I would like Firefox to work in the same manner as a word processor. Libre Office Writer, Microsoft Word, Microsoft Edge and other applications stop before punctuation marks and before each word. Firefox, on the other hand, will stop, for example, before an opening bracket but then move to the start of the second word after the bracket, not the first one. Also, it jumps over commas and full stops and other 'structural' punctuation marks, which is also odd, or at least different from what all other apps seem to do.
This may seem basic, but it can wreak havoc in my day to day work as a translator, with clients asking me to work on web-based tools more and more often. Making the spell checker able to work in two languages at the same time was huge for me, but this non-standard behaviour when moving from one word to another still keeps me from using Firefox as my default browser.