Is there any way to reduce more than the minimum width that browsers allow?

Operation System: Windows 10
Screen resolution: 1366x768

I'm trying to make the browsers even smaller in width, but they won't let me pull more to the side than this amount below, Google Chrome on the left and Firefox on the right. Is there any way to remove this block and lessen more than that?

Note: My problem is screen space on my monitor, so I needed to be able to shrink a little more the browser's.

The idea is to increase this black space between browsers and have more freedom to adjust the width without blocking the minimum.

You may cause both Chrome and Firefox to open a reduced window by launching a narrow adjustable browser window from JavaScript.

Here is the HTML page you could use:

<a href="javascript:window.open('your_url_here', '','width=320,height=480')">Open!</a>

This will display a simple page with a link named "Open!". Clicking on the link will open a new browser window that can be resized more than the usual browser page.

In my experiments, I managed to reduce Firefox to a width of about 290 pixels. Chrome I managed to reduce to about 200 pixels.

Another method for Chrome is to use the extension OSX Resizer.

Clicking the extension's icon will reopen the current page in a new adjustable window that I managed to reduce to 176 pixels.

Still another method for Chrome is to use the Developer Tools and dock them to right.

The docking is done by opening the Developer Tools and clicking the three-point menu icon:

Once the Developer Tools are docked on the right, you may drag the in-between separator to resize the page that is displayed on the left.

The minimum I managed to reduce it this way was to 150 pixels.

I can't tell how small your browser is from the screenshot but I use tool like DisplayFusion which let me split my ultrawide monitor into a few virtual screens. With that, I can then press a hot key and moved Firefox into that small screen and it resize automatically. I believe that is a way to squeeze it in.

Another tool I use is Divvy, when triggered, shows my screen in grid and I move my mouse to draw a box to indicate a screen resize size that I need. I can make Firefox really tiny with this.

Picture below is taken from the 27" monitor, not an ultra-wide and you can see how small the Firefox window is.

I haven't tried this but, in theory, it should be the same - you can install Windows PowerToys which come with an app called Fancy Zone which allows you to create zones around your screen which you can then drop an application into it by pressing SHIFT and dragging you app into the zone. This will automatically resize your application into the size of the zone which you predefined.