"Webpage not available" for some webpages but not all I can not access all webpages on my phone. While some are working fine, others simply show "Webpage not available".
This appears to be independent of the webbrowser. It's always the same webpages that won't work and they won't work with neither mBrowser nor Tint Browser and I have also experienced this on my mother's smartphone with the default browser.
This is not a matter of misspelling or being temporarily not available: I have been experiencing this for months now (not always - there were times when I was able to access those pages) and the webpages are reliably accessible from a computer.
This happens both when I am entering the URL manually as well as when clicking on a link from google.

Removing the battery or clearing Tint Browser's cache did not help.

some pages that are not accessible:


https://wiki.archlinux.org
https://github.com
https://jisho.org


some pages that are accessible:


google
leo.org
wikipedia.org


I am using Android 4.0.4 (CyanogenMod 9.1.0), mBrowser 12.0, Tint Browser 1.8 (10). My mother's phone was a Sony Experia with the preinstalled OS but I can't check the Android version because it got lost.
Let's check the supported HTTPS protocol versions of the sites you mentioned.


https://wiki.archlinux.org -> only TLS 1.2
https://github.com -> only TLS 1.2
https://jisho.org -> only TLS 1.2 
https://google.com -> TLS 1.0 TLS 1.1 TLS 1.2
https://leo.org -> TLS 1.0 TLS 1.1 TLS 1.2
https://wikipedia.org  -> TLS 1.0 TLS 1.1 TLS 1.2


Do you see the pattern? From my perspective I would assume that the used browsers use the old outdated web engine of your OS which does not support TLS 1.2. 

My suggestion would be to install the Chrome app and use it (and may be even set it as default browser engine - was this already possible on Android 4.0?). 
Chrome includes the latest SSL/TLS libraries with TLS 1.2 support furthermore it is not affected by dozens of security vulnerabilities which your outdated integrated web engine suffers from.