Short answer: no color management. You need to use a web browser with color management to get a perfect match, and the file needs to have the sRGB profile embedded. That basically means anything but Edge or Internet Explorer. All other browsers are able to handle it correctly (although some settings may need to be manually enabled).
Likewise, a lot of image viewers also lack support for color management.
Note that it's not enough to just have sRGB as your working space. The embedded document profile will always override the working space. You need to make sure the file itself is actually sRGB, and convert if it isn't.
If you use Save For Web or Export you need to check both "Convert to sRGB" and "Embed Profile". Both are (for some reason) off by default.
An image will usually look roughly right even without color management, if these two conditions are met:
- the document was created in sRGB and has sRGB numbers
- it is viewed on a monitor that is close to sRGB natively. Historically most monitors are, and that's why sRGB became the web standard. But newer / more expensive wide gamut monitors are not. These units require full color management at all times.
Just arbitrarily assigning color profiles does not constitute color management! Therein lies your answer: your own monitor is mistweaked and isn't anywhere close to standard color spaces and profiles, hence only establishing a full on CM based on resetting and un-mistweaking your monitor will produce reasonably predictable results. You have some reading to do, I believe...
Some reading to do... I hardly get what you mean comparing to the previous answer. I am french btw and it's very hard to find relatable info in french or understandable english. So no need to be harsh.
ps: I don't assign random color profiles.
Thank you for your answer I always checked both. I will check what you say but I am pretty certain I fulfilled these conditions. Thank you.