Bug with browsers' interpretation of @media queries

It's difficult to give a specific answer without seeing what you are seeing, but it's possible that the browsers are handling the transition from one media query to the next in different ways discussed below.

Most Likely Cause: Windows Display Settings

I assume you are using Windows when you mention Edge, I suspect this might be because you have changed the scale of your display in Windows - Display Settings. If this is set to 125% for example, this can have an affect on all aspects of your display.

So really this isn't a bug with the media queries, so much as a discrepancy caused by the browsers not effectively handling the scaling by Windows Display settings.

UPDATE - Now that you have confirmed that you can stop on a particular point where this happens, then I'm pretty confident this is the cause. In my testing yesterday when looking into this, I was able to reproduce that behaviour when the display was scaled.

Using the following test case with original styling of an empty block with a red border, and different CSS applied at (max-width: 1119px) and (min-width: 1120px), the issue happens only when the display is scaled.

body{ margin:50px 0 0 0;}

.test {
  border: 10px solid #f00;
  height: 10px;
}

@media (min-width: 1120px) {
  .test {
    background: #ff0;
    height: 500px
  }
}

@media (min-width: 720px) and (max-width: 1119px) {
  .test {
    margin-left: 300px;
    background: #0FF;
    height: 200px
  }
}

@media (min-width: 460px) and (max-width: 719px) {
  .test {
    margin-left: 300px;
    background: #00f;
    height: 200px
  }
}

@media (max-width: 460px) {
  .test {
    background: #ff0;
    height: 100px
  }
}

<div class="test"></div>

Firefox, using Dev Console ruler to show window size:

Display Scale: 100% (i.e. no scaling) at 1119px width - CSS works as expected*

@media (min-width: 720px) and (max-width: 1119px) {
  .test { margin-left: 300px; background: #0FF; height: 200px }
}

Display Scale 125% at 1119px width - no CSS media query applied, so CSS reverts to original

.test { border: 10px solid #f00; height: 10px; }

Possible Reason for the "glitch"

If the above is the case (or even if it isn't), I suspect your next question is why is it happening. Only the developers can answer that, but thinking logically we can come up with the reasoning below.

What are media queries meant to do?

First, we need to look at the purpose of media queries. According to the W3C CSS3 Media Queries recommendation:

The ‘width’ media feature describes the width of the targeted display area of the output device.

From this, we can assume they were intended for selecting the CSS to use depending on the media query that matches the screen/window size. Screen size can't have fractional pixels (e.g. 719.5px) and points between the whole pixels can only "exist" while the screen is being resized, and media queries are not intended to cover such temporary transitions.

OK, that's the why it isn't necessarily a "bug" and why it isn't always handled well in browsers, now...

What is causing this issue to happen during transitions?

If you have changed the scale, the browser has to recalculate the all the sizes to scale them up/down also. This "glitch" in the transition is most likely being caused by these calculations resulting in fractions of pixels. (If you haven't changed the scale, the same logic actually still applies)

It appears the browsers such as Chrome have been build to handle the recalculations/ size change in whole pixels, so the display will jump from the CSS applied by (e.g.) max-width:719px media query to the CSS for min-width:720px.

However other browsers such as Firefox don't seem to work like this and try to calculate the display based on the fractional pixels. This means there can be instances where the recalculated/changing size fall between e.g. max-width:719px nor min-width:720px.

In this case it seems to change the display to whatever CSS applies at that point - if there is another media query overlapping those sizes that would be applied, but more likely the original CSS is getting applied. So what you are seeing in that transition you describe is your CSS that exists outside of the media queries, e.g. if your CSS is written for mobile-first then you are seeing the CSS for mobile version of the site.

What can we do to "fix" it?

Aside from changing back the scale to 100% (which isn't a feasible option because you can't ask all your visitors to do that!) I don't know if there is a reliable solution.

• One option is to use decimal values in your media queries like you mentioned, e.g.

@media (min-width: 720px) and (max-width: 1119.999px) { /* CSS....*/ }
@media (max-width: 719.999px) { /* CSS....*/ }

• Another is to try is to make sure that you have suitable styling in your original CSS that will be applied at the "in-between" points, e.g. 719px - 720px.

Firefox and Edge appear to calculate and store their view port widths as floating point numbers, and media queries are applied to those values rather than the whole-pixel widths that they represent. There is consequently a difference in the way in which the parameters of our media queries are interpreted.

So whilst Chrome and Opera transition between 720 pixels and 719 pixels seamlessly, the same transition on Firefox or Edge can result in the browsers' simply skipping over the query and applying whatever default styling is otherwise relevant.

My original solution was to apply a browser-specific @media query to account for values between the whole pixels.

@-moz-document url-prefix() /* Firefox */
{
    @media only screen and (min-width: 719.000001px) and (max-width: 719.999999px)
    {

However, the real problem was the way in which I was specifying the parameters of the media queries. Unlike in programming languages, in which we can (and should) define mathematical parameters with equality and inequality (e.g. -1 ≤ x ≤ 1), CSS employs a hierarchy. For example, if @media (max-width: 600px) is followed by @media (max-width: 400px), whilst the two are not logically exclusive, the latter query will take precedence over the former.

So my solution was to change the way in which the @media queries were structured, such that there were max-width declarations only. If we try to define upper and lower limits of each interval, we run into the aforementioned problems with the way that the distinct browsers interpret the limits.

You could avoid any requirement to set up specific decimals by having no gaps between your queries at all.

For example:

(min-width 1px)      // Instead of (max-width: 719px)
(min-width 720px)    // Instead of (min-width: 720px) and (max-width: 1119px)
(min-width 1120px )  // Instead of (min-width: 1120px)

Currently, you have a middle band with one 'max-width' band and one 'min-width' band either side of it.

The above alternative solution just uses 1 direction (min-width), so there are no gaps to contend with.

Or:

That solution assumes you don't want to develop your whole front-end style for sub-720px and then media-query every larger size.

If you did want to do that, you could always just use the following: (sure Google search SEO may love you, but you may hate it!)

(min-width 720px)    // Instead of (min-width: 720px) and (max-width: 1119px)
(min-width 1120px )  // Instead of (min-width: 1120px)

You would then need to incorporate your code that you wanted to put in your max-width: 719px media query into your base ("non- media query") code.

Which one?

I'd use the first solution.

Based on the OP, that one would be more applicable in that situation too.

Actually, I wouldn't use the first solution. I'd code for, say, >1230px, and then use media queries that use max-width for the responsive steps below that.