A long time ago when entering my password a colour requester popped up (unexpectedly) and I have had this little problem since - I think.
Sometimes when reading things the colour contrast is wrong and I can hardly read what is written.
People in/on the Firefox forum have helped me with SOME of the problems.
Though I can't say I am 100% sure, but the result does look better from what I remember it being.
But the underlying problem remains.
Without wanting to start a finger pointing game, here's what I know.
In FireFox some things are near impossible to read.
Example:
I was wanting to use the cronplus node and was looking at the instructions.
You are using a dark mode theme are you not? There are likely some elements of Node-RED where the theme hasn't applied a style or possible where Node-RED still has manual styling so that the theme can't style it. The other possible issue - as Steve says - is that perhaps some nodes have applied manual styling themselves and so the theme is ignored there.
You or someone else would need to look at the mis-styled elements using the browser dev tools to find out which of these issues applies.
Nope. You have to do it via the menus.
In FF that is Settings > Privacy & Security > History section - Clear History > select Cache and Offline web site data - OK
It does not force it to reload absolutely everything. To be certain you have to go through the menus. I thought like you once, then the dashboard was misbehaving after an upgrade. Dave (I think) said basically what I have just written and he was correct. Forcing a cache clear through the menus fixed it.