I like Meld as a visual diff/merge tool. You can also use it as the default in TortoiseHg. Open TortoiseHg's Workbench. Go to File » Settings, make sure the global settings tab is active. Click Edit File, if it doesn't yet exist create a section called [extdiff], and under [extdiff] add cmd.meld = /path/to/meld. For Windows it would be something like cmd.meld = C:Program Files (x86)Meldmeld.exe. From the command line you should be able to use hg meld to get your diff shown in Meld.
Having resolved recent SSL certificate issues with Mercurial/TortoiseHG, I now encountered a similar issue with the wildcard certificate for *.google.com where getting a clone would result in a "SSL: Server certificate verify failed" error.
One way around this issue is to add the fingerprint for this certificate to your configuration. Currently for *.google.com this is 00:d5:88:35:29:b9:7f:03:92:60:c2:04:e4:b7:01:f0:07:53:15:a8 and one way to get this from a Unix command line is with openssl s_client -connect code.google.com:443 < /dev/null 2> /dev/null | openssl x509 -in cert-code -fingerprint -noout -in /dev/stdin | tr "[:upper:]" "[:lower:]". This corresponds with Chrome's certificate view's thumbprint field, you just need to add colons.
Right click in Explorer, select TortoiseHG » Global Settings and then click Edit File and add the following:
[hostfingerprints] code.google.com = 00:d5:88:35:29:b9:7f:03:92:60:c2:04:e4:b7:01:f0:07:53:15:a8
This should make Mercurial/TortoiseHG work, at least until the certificate expires and you need to update it with the latest fingerprint.
For my own development I use Mercurial and TortoiseHG for my version control system. I also use, at the moment, a CAcert certificate to use HTTPS with my repositories. I am not sure what changed when, but apparently the certificates now get verified. So this causes obvious problems trying to push or pull due to "SSL: Server certificate verify failed" errors.
To make this work on a Windows 7 machine with TortoiseHG in stalled, first download the CAcert root PEM certificate and place it some permanent directory. Next open the TortoiseHG global settings (right click somewhere in Explorer and select TortoiseHG » Global Settings). In the window that opens click the Edit File button. If it does not exist yet create a section similar to this:
[web] cacerts = C:\path\to\cacert-root.pem
Press Save and OK and any push and pull action with HTTPS URLs should work as they ought to.