The MUI spinner impacts the cpu usage.
While only a few of them don't matter, rendering multiple of them can impact the cpu usage.
This can be a problem in the reader in case a chapter with a lot of chapters is rendered and a continuous reading mode is being used.
In such a case the cpu usage stays increased until all pages have been loaded
Depending on the screen size and e.g. the set "reader width" pages might not have filled out the full img elements size due to "object-fit contain".
This was caused due to the image wrappers flex container "align-items center" which slightly reduced the images width to some ".xy" number (e.g. instead of wrappers width 258px, the images were something like 257.83px)
on firefox images are decoded async which causes a "flicker/blinking" when they're getting visible for the first time
this is an issue especially in the reader because pages that should not be shown are rendered but
not displayed, which then causes this issue once they get displayed
