Firefox: add option to always enable in Private Browsing

[veehaitch]

I was looking for a way to always use a SOCKS5 proxy when running in Private Browsing mode. This PR adds a respective option to the general settings page.

• When checked, Firefox always uses the configured proxy for requests originating from an incognito tab.
• When using the "Direct (No Proxy)" mode, the option is ignored altogether. I use the option in conjunction with the "System Proxy" mode and it works fine.
• I didn't bother adding support for Chrome. I didn't dig into it put it seems like some extra effort is required to support it.

Looking forward to reading your feedback 🙂

[salarcode]

Thanks for the PR, looks good. Having this option is a great idea. But this is not the main branch for new work, the new work for is happening under this new version branch. I'm still writing on some doc for it and will merge it to master when I get some free time...

• I didn't get why "Direct (No Proxy)" mode is not working in Firefox "incognito window"?
• Since this is overriding all modes, we definitely need to indicate this happening in popup menu with a nice ui or a replacement ui/ux.
• Chrome can support this feature so we need to ship it in same time as Firefox
• As mentioned new work in new branch

What I will do is keep this PR open and slowly bring it to the new version with above changes.

Thanks again 👍

[veehaitch]

Thanks for your response! Your proposal sounds good. Maybe even a separate configuration for incognito mode would make sense, i.e., which proxy and proxy mode should be used for incognito tabs/sessions.

I didn't get why "Direct (No Proxy)" mode is not working in Firefox "incognito window"?

This is perfectly possible and just due to my implementation. I just thought it makes sense to not honor the new option if operating in direct mode. I also wanted to have an easy way to disable the proxy even when using private browsing.

What I will do is keep this PR open and slowly bring it to the new version with above changes.

Awesome, this sounds great. Feel free to reach out if you want me to test your progress.

[salarcode]

@veehaitch The 'Private Browsing Profile' feature which is similar to this one is added in alpha version. Check here #213. Please test if you can, thanks.