According to this House of Commons Library research paper, suffrage in the county constituencies was initially open to every man who was head of a household, or at least that's my understanding of the phrase every free inhabitant householder, freeholder and non-freeholder. I assume that free means men who were not villeins.
Universal male suffrage had some popular support from at least the time of the English Civil War in the 1640s. Were there riots, protests, or anything of the kind when parliament took away the right to vote from all these people? 'Hundreds of thousands' is a guess, of course. According to Wikipedia's demography of England page there were under 3 million people in England at the time.
Before 1430 there is evidence that the right to vote for the knights of the shires in English county elections was given to “every free inhabitant householder, freeholder and non-freeholder”. There was no requirement for freeholders to be landed freeholders; the freehold could relate to something other than land.
In the late fourteenth century and early fifteenth there were calls for shire elections to be restricted to the “better folk of the shires” but the official view remained that the common assent of the whole county was required. Election meetings could be large and lively and feuds between factions sometimes spilled over to election meetings.
In 1429, a petition was presented to the King by the Commons which expressed concern that some elections had involved “too great and excessive number of people...of whom the greater part are by people of little or no means” and that these people “pretend[ed] to have an equivalent voice...as the most worthy knights or esquires dwelling in the same counties”. The petition called for the vote to be restricted to those freeholders resident in a county with a freehold value of 40 shillings a year. A freehold was not restricted to land; it could refer to many types of property.
The petition led, in 1430, to such a statute being passed and all leaseholders, regardless of the value of their leased land, were stripped of the vote.