Narrowed down the issue to `-ms-`-prefixed properties not showing up for **inherited** properties in the Rules panel. But I'm not sure that the behavior is wrong, though. Details below.
First, the updated STR:
1. paste this in the address bar:
```
data:text/html,<style>html {font-size:1em;-webkit-text-size-adjust:100%;-ms-text-size-adjust:100%;}</style>
```
2. open DevTools and inspect the `body` element
3. notice the inherited properties from the `html` element (the `-ms-text-size-adjust:100%;` declaration is missing).
4. delete all declarations for the `body {}` rule
5. switch to the Changes panel and click on Copy Rule for the changed `body{}`
6. paste the clipboard into a text file.
The original issue isn't a bug, as explained in [Comment 2](https://bugzilla.mozilla.org/show_bug.cgi?id=1538728#c2). The _Copy Rule_ button copies the result of the changed `html {}` rule whereby the `-ms-text-size-adjust:100%;` is the only thing remaining because it didn't show up in the Rules view to be deleted.
The reason why I think **not showing** the `-ms-text-size-adjust:100%` declaration as inherited **is correct** is that it's not supported by Firefox so it can't be inherited. Likewise, `-webkit-text-size-adjust` is not supported either. Showing it is wrong as well. The only inherited declaration in this scenario is `font-size: 1em`.
Pinging Martin Balfanz (PM) to double-check my interpretation and confirm if we should log a separate bug for the misleading inherited prefixed properties. Also to draw attention to the example of a user who confuses what _Copy Rule_ button does and whether we need to adjust the UX.
Bug 1538728 Comment 3 Edit History
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Narrowed down the issue to `-ms-`-prefixed properties not showing up for **inherited** properties in the Rules panel. But I'm not sure that the behavior is wrong, though. Details below.
First, the updated STR:
1. paste this in the address bar:
```
data:text/html,<style>html {font-size:1em;-webkit-text-size-adjust:100%;-ms-text-size-adjust:100%;}</style>
```
2. open DevTools and inspect the `body` element
3. notice the inherited properties from the `html` element (the `-ms-text-size-adjust:100%;` declaration is missing).
4. delete all declarations for the inherited `html {}` rule
5. switch to the Changes panel and click on Copy Rule for the changed `html {}`
6. paste the clipboard into a text file.
The original issue isn't a bug, as explained in [Comment 2](https://bugzilla.mozilla.org/show_bug.cgi?id=1538728#c2). The _Copy Rule_ button copies the result of the changed `html {}` rule whereby the `-ms-text-size-adjust:100%;` is the only thing remaining because it didn't show up in the Rules view to be deleted.
The reason why I think **not showing** the `-ms-text-size-adjust:100%` declaration as inherited **is correct** is that it's not supported by Firefox so it can't be inherited. Likewise, `-webkit-text-size-adjust` is not supported either. Showing it is wrong as well. The only inherited declaration in this scenario is `font-size: 1em`.
Pinging Martin Balfanz (PM) to double-check my interpretation and confirm if we should log a separate bug for the misleading inherited prefixed properties. Also to draw attention to the example of a user who confuses what _Copy Rule_ button does and whether we need to adjust the UX.