I've just checked, and 22 out of 29 Dock icons on my Mojave system are not the standard rounded-square. My opinion is that different shapes, like differing colours, can be an aid to quickly identifying the icons.
This has already been posted to the Bugzilla group, Square icon for macOS Big Sur but the thread has since been closed as there was no value added and it seems it's not a huge priority for them based on my contribution and following of the thread.
That's odd. I just looked and had three custom icons. I removed two (old) ones and left Firefox. I never notice these icons as different when looking for something and wouldn't be able to have told you who or how many I had, other than obviously one was Firefox. Put me down as the silent majority(?) that don't care.
@edumorlom, It's just an icon and I'm sure they have other priorities.
Check out MacOSicons.com and search for Firefox, click the icon you want to download and then go to Firefox in your Applications folder, right click on it and select Get Info. Then drag the icns file you just downloaded to the current icon in the get info window. Problem solved.
It's great to hear your thought on updating the Firefox icon(s).
Our team is currently working on it, and all the Firefox browsers will soon have a square-round icon for macOS. This will meet the Apple icon guideline.
Thank you for providing your idea and feel free to ask any questions meanwhile.
I should mention that there is a "standard" scaling for circular macOS icons within Apple's design guidelines, which both Safari and Chrome already follow. I hope Firefox's macOS icon will be scaled the same — as it will fit in with other icons on the platform. Here is an image demonstrating the alignment:
Standard sizes for circular icons in macOS 11+ are as follows:
actual resolution
@1x
@2x
circle width / height
1024x1024 px
N/A
512x512@2x
710x710 px
512x512 px
512x512@1x
256x256@2x
356x356 px
256x256 px
256x256@1x
128x128@2x
178x178 px
128x128 px
128x128@1x
N/A
88x88 px
64x64 px
N/A
32x32@2x
44x44 px
32x32 px
32x32@1x
16x16@2x
20x20 px
16x16 px
16x16@1x
N/A
10x10 px
Also, after testing various background colors for the icon on different wallpapers and within the context of other macOS icons, this gradient (composed of three colors from Firefox's brand palette — #9059FF, #7543E3, & #582ACB) feels by far the most natural imo: