It took me a while to get my XP games to run on Win7. That is precisely one of the many reasons I have NOT gone to Win10.
I have never understood software companies who remove features from their software programs in later upgrades/updates. Many times, the feature they removed was the exact reason I was using their program. I have dropped many software programs over the years for removing or changing features. The next task it in finding a good replacement, but for many features, comparable replacements do not exist.
I have several old (XP and Win98) programs and utilities that have no comparable equivalents in the Win7/10 world.
I usually use an old IE6-based tabbed browser for FR. It has several editing add-on utilities that are not available with other browsers. When FR ‘fixed’ the security certification issue several months ago, that broke IE. I had a computer reboot due to electrical surge and it ‘lost’ my IE log-in to FR. The problem is when the HTTP log-in screen tries to switch to an HTTPS secure page. The problem does not happen with Opera, FF, Chrome.
Then, there is Firefox and the rapid release. I have lost many good utility extensions/add-ons because the original creators stopped trying to update to Mozilla’s rapid release. I recently read that by upgrade 57, FF will completely redo their add-ons programming, so likely by then all existing add-ons will no longer be compatible.
New, Improved are not always better. I still cringe every time I see ‘upgrade’ or ‘update’ and wonder what THAT will break.
Have you looked at SeaMonkey lately (I haven't - I have a really old version that I've been afraid to update). It may have features that have been cut out of the newer programs.
As for Firefox - it's like the guys running it are trying their best to kill it. At least Microsoft is pursuing a clear agenda, even if I don't like it as a consumer (they do seem to be delivering for their stockholders).
Sorry, but IE 6 on XP simply isn't capable of using sha-2 certificates, a fact due to the design of the operating system and IE. Earlier hashing algorithms (md5, sha) are simply insecure at this point in time, and using web browsers that only support these older security implementations is dangerous. IE 6 uses Windows XP's security mechanisms, which are completely insecure at this time. Other browsers don't have that limitation.
Microsoft has been notoriously slow at implementing security upgrades, for the simple reason that they're "inconvenient." Even in Windows 7 and Windows Server 2008R2, TLSv1.2 (a security mechanism that is considered secure,) is optional, and is something of a PITA to implement.
Mark